gun manual
TRANSCRIPT
Distribution authorized to U.S. Gov't. agencies and their
contractors; Administrative/Operational Use; FEB 1970. Other
requests shall be referred to Army Materiel Command, Alexandria,
VA. Document partially illegible.
USAMC ltr, 14 Jan 1972
' £ * & &
-aiiv 3
A M C A M P H L E T M C P 706-260
ENGINEERING DESIGN
GUNS ERIES
A U T O M A T I C W E A P O N S
m
o «70
H E A D Q U A R T E R S , . S . R M Y M A T E R I E L O M M A N D E B R U A R Y 9 7 0
Ipiiir
No. 706-260
H E A D Q U A R T E R S
UNITED S T A T ES R M Y A T ER I E L O M M A N D
WASHINGTON. D . . 0315
ENGINEERING ES IGN A N D B O O K
AUTOMAT IC E A P O N S
5 February 1970
Paragraph
1-1
1-2
1-3
1-4
LIST O F I L L U S T R A T I O N S
LISTOFTABLES
PREFACE
C H A P T E R . N T R O D U C T I O N
G E N E R A L
D E F I N I T I O N S
D E S I G N P R I N C I P L E S FOR A U T O M A T I C W E A P O N S
Page
\i
viii
x
1-1
1-1
1-1
1-1
C H A P T E R 2. B L O W B A C K W E A P O N S
2-1 G E N E R A L
-1
2-2 SIMPLE B L O W B A C K -3
2—2.2.2 Counterrecoil Time -6
2-2.2.3 Total Cycle Time -7
2-2.3 E X A M P L E O F IMPLE B L O W B A C K G U N -8
2-2.3.1 Specifications
-8
2—2.3 .3 Case Travel During Propellant G as Period -10
2-2.3.4 Sample Problem of Case Travel
— 11
2-3 A D V A N C E D PRIMER I G N I T I O N B L O W B A C K -12
-12
2-3.2 A M P L E C A L C U L A T I O N S OF A D V A N C E D
PRIMER I G N I T I O N -13
2-3.2.1 Firing Rate
— 15
-17
-17
2-4.2 D Y N A M I C S O F D E L A Y E D B L O W B A C K -18
2-4.3 P R O B L E M FOR D E L A Y E D
B L O W B A C K A C T I O N -24
2-4.3.1 Specifications
2-4.3.2 Design Data -24
2-4.4 O M P U T E R ROUTINE FOR C O U N T E R R E C O I L I N G
B A R R E L D Y N A M I C S -33
2-4.5 S P R I N G S
-40
TABLE F O N T E N T S Con't.)
Paragraph ag e
2-5.2 D Y N A M I C S O F RETARDED B L O W B A C K -40
2—5.2.1 Kinematics of the Linkage
the Dynamic Analysis
— 44
2-6 R A T I N G O F B L O W B A C K W E A P O N S -47
C H A P T E R 3. R E C O I L - O P E R A T E D
3-1 G E N E R A L
-1
_i
3-3 S A M P L E P R O B L E M _LONG R E C O I L M A C H I N E G U N .. -1
3-3.1 S P E C I F I C A T I O N S _1
3-3.2 DESIGNDATA -1
_9
3-5 SAMPLE P R O B L E M _ S H O R T R E C O I L M A C H I N E G U N -9
3-5.1 S P E C I F I C A T I O N S _9
3-5.2 DESIGNDATA -9
3-6 A C C E L E R A T O R S _15
3-7 SAMPLE P R O B L E M ACCELERATOR -17
3-7.1 S P E C I F I C A T I O N S -17
3-7.2 DESIGNDATA -17
3-8 R A T I N G OF R E C O I L - O P E R A T E D G U N S -21
C H A P T E R 4. A S - O P E R A T E D W E A P O N S
4-1 GENERALREQUIREMENTS -1
-1
-1
4-3.1 M E C H A N I C S OF T H E Y S T E M _i
4—3.1 .1 G as Filling Period _g
4-3.1.2 Bolt Locking C am
4—3.1.3 C am Curve — 15
4-3.2 A M P L E P R O B L E M FOR C U T O F F E X P A N S I O N
SYSTEM
4-3.2.5 Recoil Time
— 24
4-3.3 IGITAL C O M P U T E R ROUTINE FOR C U T O F F
E X P A N S I O N
4-3.3.2.1 Bolt Unlocking During Helix Traverse -29
4-3.3.2.2 Bolt Unlocking During Parabola Traverse -29
4-3.3.2.3 ol t Unlocked, Bolt Travel ing With
Operating Rod — 31
Paragraph ag e
4-3.3.3.1 Recoil Dynamics
-37
-38
4-4.1 S A M P L E P R O B L E M -38
4-4.1.1 Specifications
4-4.1.4 Spring Design Data -45
C H A P T E R 5. REVOLVER-TYPE M A C H I N E G U N S
5-1 SINGLE B A R R E L T Y P E -1
5-1.1 P R E L I M I N A R Y D Y N A M I C S OF FIRING C Y C L E -2
5—1.1 .1 ample Problem of Preliminary iring Rate Estimate . -7
5-1.1.2 Analysis of C am Action
5-1.1.2.2 Driving Spring
-18
5_1.2 INAL E S T I M A T E OF THE C O M P L E T E FIRING C Y C L E -18
5—1.2.1 ontrol of Recoil Travel During Propellant G as Period . -20
5-1.2.2 Operating Cylinder Design
Cylinder Action -31
5 — 1.2 .4 Sample Calculation for Complete Firing Cycle -32
5-1.2.4.1 Counterrecoil Time of Recoiling Parts -33
5-1.2.4.2 igital Analyses of Barreldrum -37
5-1.2.4.3 Firing Rate Computation -39
5-2.1.2 Loading and Ejecting
— 48
5-2.2.3 Digital Computer Program for Firing Cycle -52
C H A P T E R 6. M U L T I B A R R E L M A C H I N E G U N
6-1 GENERAL
-1
6-2 B O L T O P E R A T I N G C A M D E V E L O P M E N T -1
6-2.1 CAMACTION
6-2.1.2 Definition of Symbols
Paragraph ag e
-7
6-2.3 I L L U S T R A T I V E P R O B L E M -9
6-2.3.1 am Analysis During Feed, Rotor at Constant Velocity .. -9
6-2.3.2 am Analysis During Ejection, Rotor at Constant
Velocity
6—2.3.3 C am Analysis During Rotor Acceleration — 1 2
6-2.3.4 Program for Gun .... -13
6-3 ATING O F G A S - O P E R A T E D N D E X T E R N A L L Y
POWEREDGUNS -14
C H A P T E R 7. C O M P O N E N T DESIGN
7-1 G E N E R A L
7_2 FEED M E C H A N I S M D E S I G N -1
7-2.1 M A G A Z I N E S -2
7—2.1.1 B ox Magazines
7-2.1.2.1 Flat Tape pring
-8
7-2.2 B O L T - O P E R A T E D FEED Y S T E M -9
7_2.3 ROTATING FEED M E C H A N I S M -10
7-2.3.1 Recoil-operated Feed Mechanism
7_2.4 LINKLESSFEED Y S T E M
7-2.4.2 Example Problem for Power Required -21
7 - 3 EXTRACTORS, E J E C T O R S , A ND BOLT LOCKS ~
24
7-3.2.2 Sample Problem of Ejector Dynamics -27
7-3.3 BOLTLOCKS
30
-32
7_4.1 C O M P O N E N T S , T Y P E S , A N D A C T I O N -32
7-4.1.1 Trigger Pull
-40
7_s'.2 D E S I G N R E Q U I R E M E N T S -40
7-6 M O U N T S
-
44
7_6.1 G E O M E T R Y A N D R E S O L U T I O N OF F O R C E S -44
7-6.2 S A M P L E P R O B L E M -
8
C H A P T E R 8. L U B R I C A T I O N O F M A C H I N E G U N S
3-1 ENERALCONCEPT
3-1
3-2 X A M P L E S O F L U B R I C A N T S -1
8-3 ASELUBRICANT ~
T A B L E F CONTENTS Con't.)
A P P E N D I X E S
No. Title
A-3 Flow Chart for Retarded Blowback -6
A^l Listing for Retarded Blowback Program — 9
A— 5 Flow Chart for Cutoff Expansion — 12
A-6 Listing for Cutoff Expansion Program — 15
A-7 Flow Chart for Operating Cylinder -20
A-8 Listing for Operating Cylinder Program — 22
A— 9 Flow Chart for C am and Drum Dynamics During Recoil . — 26
A — 1 0 Listing for C am and Drum Dynamics During Recoil — 30
A — 1 1 lo w Char t for C am and Drum Dynamics During
Counterrecoil
— 35
A — 1 2 isting for C am and Drum Dynamics During
Counterrecoil
— 38
A — 1 3 Flow Chart for Double Barrel Machine Gun — 43
A — 1 4 Program Listing for Double Barrel Machine Gun — 46
A-15 Flow Chart for Multibarrel Power -52
A — 1 6 Program Listing for Multibarrel Power — 59
B utomatic Control of Rounds in a Burst for
Weapon Effectiveness — 1
LIST OF LLUSTRATIONS
Fig. No. Title
2— 3 llowable Case Travel — 4
2— 4 ressure-time Curve of C al 45(11.42 mm) Round — 8
2— 5 chematic of Advanced Primer Ignition ystem — 13
2— 6 ocking System for Delayed Blowback — 18
2— 7 ressure-time Curve of 2 0 mm Round — 25
2— 8 chematic of Retarded Blowback Linkage — 40
2— 9 inematics of Retarded Blowback Linkage — 41
2 — 1 0 ynamics of Bolt and Linkage — 42
3— 1 chematic of Long Recoil ystem — 2
3— 2 chematic of Short Recoil ystem
4-3 otating Bolt Lock an d Activating C am -11
4-4 orce ystem of Bolt C am -12
4_5 ressure-time Curve of 7.62 mm Round — 18
4_6 perating Distances of Moving Parts
5— 1 chematic of Single Barrel Revolver-type Machine Gun .... — 1
5_2 wo tage Ramming _2
5— 3 orce Diagram of Recoiling Parts and lide — 3
5_4 chematic of C am Geometry — 5
5_5 am-slide Force Diagrams — 9
5— 6 ingle Barrel Drum Loading Diagram — 10
5_7 ingle Barrel Drum Dynamics
5-8 nterior Ballistics of 2 0 mm Revolver-type Gun -19
5_9 xtractor Assembly With Antidouble Feed Mechanism .... — 35
5 — 1 0 xtractor C am Assembly — 36
5 — 1 1 ocation of Basic Operations — 47
5—12 chematic of Double Barrel Drum-cam Arrangements — 47
5—13 chematic of Ammunition Feed ystem — 48
5 — 1 4 chematic of Ammunition Magazine
5_16 ouble Barrel Drum Loading Diagram — 51
5—17 ouble Barrel Drum Dynamics — 51
5 — 1 8 orce-time Curve of 2 0 mm Revolver-type Gun — 53
5 — 1 9 eometry of C am Actuating Lever
— 2
6— 2 oading Diagram of Bolt and C am During Acceleration . — 2
6_3 eed Portion of C am
— 3
6— 4 oading Diagram of Bolt and C am During Deceleration . — 7
6— 5 olt Position Diagram for Computer Analysis — 13
Fig. No. Title
age
7-1 nitial Contact of Bolt an d Cartridge Case Base _i
7-2 hamber-projectile Contact -2
7-3 ox Magazine -2
7-6 eometry of Double R ow tacking _4
7— 7 ox Magazine Follower — 4
7-8 lat ap e pring an d Loading Analogy _5
7-9 ectangular Coil Spring an d Loading Characteristics _7
7-10 chematic of Feed ystem. End View -10
7-11 eed ystem Illustrating Mechanics of Operation -11
7-12 ecoil-operated Rotating Feed Mechanism -13
7-13 eed Wheel an d Operating Lever Units -14
7-14 lectrically Operated Rotating Feed Mechanism -15
7-15 uter Drum -16
7-16 nner Drum Helix
7-18 chematic of Linkless Feed ystem -18
7-19 ath of Rounds in ingle End ystem -19
7-20 xtractors -25
7-24 liding Breech Lock _31
7-25 ipping Bolt Lock -32
7-26 iring Mechanism for Recoil Machine G un — 33
7-27 iring Mechanism for Gas-operated Machine Gun -34
hree-position Firing Mechanism
7-30 mmunition Link. al .5 0 Round
7-31 ose Fanning Flexibility. .6 2 mm Link — 42
7—32 as e Fanning Flexibility. 7.62 m m Link — 43
7-33 eometry of Base Fanning — 44
7-34 elical Flexibility. .6 2 mm Link -45
7-35 otal Folding .6 2 mm Ammunition Belt -46
7-36 artial Folding 7.62 mm Ammunition Belt -46
7—38 oading Diagram of Mount -47
Table No. Title
ag e
2- 1 as e Travel of C al 45(11.42 mm) G un -11
2-2 ecoil Travel of 20 mm Gun
2-4 nput for Delayed Blowback Program -37
2-5 ounterrecoil Dynamics of Delayed Blowback Gun -38
2-6 ymbolcode Correlation for Retarded Blowback -46
2-7 nput Data for Retarded Blowback -47
2-8 etarded Blowback Dynamics -48
3-1 ecoil Travel of 20 mm Gun
3-2 pring Design Data of Recoil-operated Guns -8
3-3 ecoil Travel of 2 0 mm Gun Equipped With Accelerator .. -17
4-1 omputed Dynamics of G as Cutoff System — 25
4-2 as Expansion Time Calculations -29
4-3 ymbolcode Correlation for Cutoff Expansion — 30
4-4 nput for Cutoff Expansion Program -31
4-5 omputed Dynamics Before G as Cutoff -32
4-6 omputed Dynamics After G as Cutoff Bolt Unlocking
During Helix Traverse
During Parabola Traverse
an d Rod Unit Recoiling After C am Action -34
4-9 omputed Dynamics. Counterrecoil Bolt Locking
During Parabola Traverse
-46
5— 1 ree Recoil Data of 2 0 mm Revolver-type Machine Gun .. — 21
5-2 reliminary Recoil Adapter Data
5-4 perating Cylinder Data for 0 .12 n.
2
2
2
2
5-9 ymbolcode Correlation for C am Dynamics -38
5_10 nput Data for Drum Dynamics During Recoil -38
5-11 nput Data for Drum Dynamics During Counterrecoil .... -39
5-12 omputed Recoil an d Operating Cylinder Data for
Orifice Area of 0.042 in .
2
-40
5-14 am and Drum Dynamics During Counterrecoil -42
5_15 ymbolcode Correlation or Double Barrel Machine Gun .. -56
5-16 nput Data for Double Barrel Machine Gun -56
5-17 ouble Barrel Machine Gun Dynamics — 59
VII
Table No. Title
Multibarrel Gun -14
Power
7-1 Power Required fo r Linkless Belt Feed System -24
7-2 Firing Pin Dynamics -40
A
recoil travel
= bore area
case nd hamber; perating ylinder
piston area
»c r
= orifice area
C
r
major xi s f lliptical am ; ength f D
short segment of rectangular coil spring
= average linear acceleration
= cceleration of chutes
d
ca m path
p
acceleration
= or : 1 acceleration of ca m roller on ca m
path
a
at
travel; ollective erm n efining ime
during polytropic expansion of ga s
=minor xi s of an elliptical cam; length of
long egment of ectangular oi l pring;
spring width
elliptical ca m
ca m
= orifice coefficient
rear support
= drum diameter
= wire diameter
operating cylinder
= differential time
= differential distance
and driving springs
J
crb
gas cutoff
= counterrecoil energy
= counterrecoil nergy f barrel t nd of
buffer action
ment
= energy of rotating parts, drum energy
= counterrecoil energy of drum
= energy of drum-slide system
= ejection energy of case
= energy of operating rod
=energy f ecoiling arts; nergy o e
absorbed by mount
spring; driving spring energy
of unlocking of bolt
slide
E = energy loss attributed to spring system
E = total energy loss caused by friction
energy loss in drum
energy loss in slide
base of natural logarithms
force; pring force t beginning of recoil
= general expression for average force; aver-
ag e riving pring orce; xial nertial
force
= buffer spring force
= operating cylinder force
force, entrance orce, maximum extractor
load to clear cartridge case
= effective force on barrel
gas force
on bolt
of recoil
:
ob
r
obs
sh
tb
spring
adapter
in g load
= initial buffer spring force
= ca m roller pin load
= average force during recoil
cartridge case or round
force
reaction of trigger spring pin
= average adapter force or time intervals
= barrel spring force at end of propellant ga s
period
pulse
to surge time
= command height
intersection
mass moment of inertia
=mass oment f nertia f drum; mass
moment of inertia of al l rotating parts
= effective mass moment of inertia of drum
= area polar moment of inertia
= pring constant, general; driving pring
constant
= buffer spring constant
springs
adapter
tion
= ratio of specific heats; radius of gyration;
bolt polar radius of gyration
= general xpression or lengths; ength of
recoil; bolt travel; length of flat spring
:
:
total peripheral length of ca m
:
travel
:
= length of round; ength of rear pintle leg
= appet travel; barrel spring operating
deflection
bending moment
= effective mass of ammunition
belt; effective mass of rotating drum
:
:
:
first bend of flat tape spring
:
:
:
curve; ormal orce on roller; number of
rounds; number of active egments in flat
spring
of links of ammunition
:
:
:
:
general erm or pace between ounds
(pitch)
:
= . critical pressure
muzzle
Pu
cartridge case
R
a
round
R,
= distance from ca m contact point o drum
axis
= roller radius; rack eactions du e to ota-
tional forces
ger reaction on sear
= mean radius of case
= distance from tipping point on ri m to C G
.ofcase
= extractor radius
= triker radius
s
a
during recoil
= utoff distance
= dwell distance
time
recoil
tion here lide ontacts as perating
unit
= travel component ue o change in veloci-
ty
torque of trigger spring
= compression time of spring
an d case
= locking lug torque
= required retainer torque
= ccelerating torque
= esisting torque
= pplied torque
= buffer time
action
contacted
= duration of propellant ga s period
=time nterval of well between ounter-
recoil an d recoil
= recoil time of bolt
= recoil time of barrel during pressure decay
after bolt unlocking
= thickness of spring
:
:
:
:
= final volume in gas equations
:
velocity f chutes; linear ejected velocity
of cartridge case
:
accelerating travel
tridge case at ejection, velocity of transfer
unit
= weight of round
= wall atio of case; weight of ga s in cylin-
der; weight of propellant charge
= weight of cartridge case; weight of empty
case
:
= total eight f propellant r propellant
ga s
ponents
= weight of projectile
weight; weight of spring
= weight of slide with 2 rounds
=weight of lide, ounds, nd as oper-
ating unit
= barrel weight
of flat spring
= width of cam
inx-direction
= bolt ravel at en d of propellant ga s period
= axial length of parabola
period; ecoil ravel f drum nd barrel
assembly
= ounterrecoiling ravel uring mpulse
= travel of recoiling parts during ca m dwell
period
= barrel travel during free recoil
= barrel travel during propellant ga s period;
after buffer engagement; recoil travel dur-
in g ca m dwell period
LIST F YMBOLS (Con't.)
peripheral length of constant slope of ca m
y
m
deflection
of rotor
y orrection factor
At time differential
Av velocity differential
Ax distance differential
of one spring segment
e
b
spring
0 = angular shear deflection
8 = ngular moment deflection
helix
P
P
2
= Poisson's ratio
= ummation
= angular velocity
P R E F A C E
This handbook s on e of a eries on Guns. t is part of a group of handbooks covering
the ngineering rinciples nd fundamental data eeded n he development of Army
materiel, which as , group) onstitutes he ngineering Design Handbook eries. hi s
handbook presents nformation on he undamental operating principles nd design of
automatic weapons nd pplies pecifically o utomatic weapons of all ypes uch as
blowback, ecoil-operated, as-operated, nd xternally owered. hese nclude ingle,
double, multibarrel, nd revolver-type machine guns and range from the imple blowback
to he ntricate M 6 1 A 1 Vulcan nd Navy 0 mm Aircraft G un Mark II M od Machine
Guns. Methods re advanced for preparing engineering design data on firing cycle, spring
design, ga s dynamics, magazines, oaders, firing pins, tc. A ll components ar e considered
except tube design which appears in another handbook, A M C P 706-252, G un Tubes.
This handbook wa s prepared by The Franklin Institute, Philadelphia, Pennsylvania, for
th e Engineering Handbook Office of Duke Universi ty, prime contractor to the U.S. Army,
and wa s under he echnical guidance nd coordination of a special subcommittee with
representation from Watervliet Arsenal, Rock Island Arsenal, an d Springfield Armory.
The Handbooks ar e readily vailable to ll elements of A M C including personnel nd
contractors having a need nd/or requirement. he Army Materiel Command policy is to
release hese ngineering esign Handbooks o ther D O D ctivities nd heir on -
tractors, nd other Government gencies n ccordance with urrent Army Regulation
70-31, dated 9 September 1966 . Procedures for acquiring these Handbooks follow:
a. ctivities within A M C nd other D O D agencies should direct their request on an
official form to :
Letterkenny Army Depot
A T T N : M X L E - A T D
Publications Distribution Branch
Chambersburg, Pennsylvania 1 7 2 0 1
b. ontractors ho av e epartment f efense ontracts hould ubmit heir
request, hrough heir ontracting officer with proper justification, o the ddress indi-
cated in par. .
c. overnment agencies other than D O D having need for the Handbooks may submit
their request irectly o the Letterkenny Army Depot, as indicated in par. above, or to :
Commanding General
Washington, D. C. 0315
Cameron Station
d. ndustries not having a Government contract (this ncludes Universities) must for-
ward their request to:
ATTN: MCRD-TV
Washington, D. C. 0315
e . ll foreign requests must be ubmitted through the Washington, D . C. Embassy to:
Office of the Assistant Chief of Staff for Intelligence
ATTN: oreign Liaison Office
Department of the Army
Washington, D. C . 0 3 1 0
All requests, ther than those riginating within theDOD, must be accompanied by a
validjustification.
Comments and suggestions on this handbook re welcome and should be addressed to
Army Research Office-Durham, Box CM , Duke Station, Durham, N. C . 27706.
xix/xx
INTRODUCTION*
This andbook resents nd iscusses rocedures
normally practiced for the design of automatic weapons,
an d explores the problems temming from the functions
of each weapon nd ts omponents. t s ntended o
assist and uide he esigner of utomatic weapons of
the un type, nd o ontain pertinent design informa-
tion and references.
1-2 GENERAL
T he purpose of the handbook s (1 ) o cquaint ne w
personnel with he many hases of utomatic weapon
design, nd 2 ) o erve s seful eference or he
experienced ngineer. t oe s ot uplicate aterial
available in other handbooks of the weapon series. Those
topics which re presented n detail in other handbooks
ar e discussed here nl y n a general sense; consequently,
the eader must depend on the referenced handbook for
the etails. nless epetitive, he ext or yclic
analyses, ime-displacement T-D) urves, hamber
design, trength equirements, prings, ams, nd rive
systems ncludes mathematical nalyses mbodying
sketches, urves, nd llustrative roblems. opics such
as ammunition characteristics, lubrication, handling and
operating features, nd advantages an d disadvantages ar e
generally escribed or e ualitatively han uantita-
tively.
weapon ffectiveness n he point ire od e — a facet
which the gu n designer ma y wish to consider.
1-3 DEFINITIONS
An automatic weapon is a self-firing gun. T o be fully
automatic, he weapon must load, fire, extract, an d eject
continuously fter the first round s loaded nd fired -
provided hat he iring mechanism s el d nlocked.
Furthermore, he utomatic weapon derives all its oper-
ating nergy rom he propellant. om e weapons av e
external power units ttached nd, lthough not uto-
matic in the strictest sense, ar e still classified as such.
There re three eneral classes of automatic weapons,
all efined ccording o heir ystem f peration,
namely: lowback, as-operated, nd ecoil-
operated'**
mechanism that uses propellant ga s pressure to force the
bolt to he ear; barrel nd receiver remaining relatively
fiied. he ressure orce is transmitted irectly by he
cartridge as e base to he bolt.
b. as-operated s the system that uses the propellant
gases hat av e een vented rom he bore o r ive
piston inked o he olt. he oving iston irst
unlocks the bolt, then drives it rearward.
c. ecoil-operated is the ystem that uses the energy
of the recoiling parts to operate the gun.
Each ystem as ariations hat ay orrow ne r
more perational eatures rom he thers. hese
variations, s well s he asic ystems, re iscussed
thoroughly n later chapters.
WEAPONS
round f mmunition, s ssentially he am e s ny
other un . ts basic ifference s having the bility o
continue iring many ounds rapidly nd automatically.
A n outer stimulus is needed nl y o tart or stop firing,
unless he atter ccurs hen mmunition upply s
exhausted. he utomatic eatures require major effort
in esign nd evelopment. he esign philosophy as
been established, then the gu n is to fire as fast as required
without tressing ny omponent o he xtent where
damage an d therefore malfunction is imminent.
An xtremely hort iring ycle eing asic, he
designer must exploit to he fullest he inherent proper-
ties of each type of automatic weapon. Generally, each
type ust eet ertain equirements n ddition o
*Prepared by Martin Regina, Franklin Institute Research
Laboratories,Philadelphia,Pennsylvania.
1-1
ments or design features are:
1 . Jte part of the vailable energy of the propellant
gases without materially affecting the ballistics.
2 . ir e ccurately t a sustained rate compatible with
the required tactics.
5. Have a mechanism that is:
a. imple to operate
6. Have positive action for feeding, extracting, ject-
ing.
ments ut o egree ormally imited y ype f
weapon. onflicting equirements re resolved by om -
promise.
1-2
C H A P T E R 2
BLOWBACK WEAPONS
Controlling he esponse of the cartridge case to the
propellant as ressure s the asic esign riterion f
blowback eapons. he ase esponds by ending o
move earward nder he nfluence of the xial orce
generated by he as pressure on ts base. Meanwhile,
because of this same pressure, the case dilates to press on
th e nner wall of the hamber. he axial force tends to
push he bolt earward, opposed only by he esistance
offered by he bolt nertia nd the rictional resistance
between ase and chamber wall. T h question no w arises
as to which response redominates, he mpending axial
motion r he rictional esistance nhibiting his
motion.
typical ressure-time urve f ound of ammunition.
3U
45
40
a.
CC
2-1
For implicity, ssume nity or bore re a nd bolt
weight. According o ig. — 1, he maximum pressure
of 5,000 si evelops n . 0005 ec. gain or
simplicity, assume that he ressure varies linearly rom
t o . 0005 ec. he ressure/» t ny im e
during he nterval
'-(jra)'- ''»*'
(2-1)
T he corresponding force F driving the cartridge case an d
bolt rearward is
where A
but,by assumption, A
b
but
J t
Integration of Eq. — 7 yields
(2-8)
2
0 .
Assume hat he imiting learance etween ase nd
chamber s qual o he ase dilation s t eaches the
ultimate trength, and assume further that the artridge
case as nominal outside diameter of .5 n. , wall
thickness of 0.05 n. , an d an ultimate trength of 50,000
psi. hen, ccording o he hin-walled ressure vessel
formula, he ressure t hich ailure mpends nd
which presses the ase firmly against the chamber wall is
Pu
o
t
t
r
50,000x0.05
t
c
a
t
, ensile tress
From q. 2 — 1 , s he ime lapsed o each his
pressure.
Pu
t
sec (2-10)
From q. — 8, s the distance that the as e and bolt
travel during this time, .e., when only the inertia of the
system is considered.
15
prevail, he artridge as e carcely oves efore
frictional esistance egins o ake ffect. Motion will
continue until E q. 2—11 is satisfied.
A
b
where
case an d chamber
Pi interface pressure of case an d chamber
ß coefficient of friction
an approximate interface pressure p
t
by quating the inside deflection of the chamber, due to
this ressure, o he utside deflection of the cartridge
case, ue o both interface and propellant as pressure,
when both case an d chamber ar considered cylindrical.
Solve for the interface pressure.
2p
W . wall ratio of case
v Poisson's atio assumed o be qual for
both materials)
unsupported artridge cases to the limit of their strength
are easonably lose o he difference in propellant as
pressure an d computed interface pressure. Thus
Pu * P-Pi
exceeds ase ecovery fter as ressures ubside;
otherwise, nterference evelops, i.e., lamping the ase
to he chamber wall an d rendering extraction difficult*.
2-2 SIMPLE B L O W B A C K
Simple lowback s he ystem herein ll he
operating nergy s erived rom blowback with he
inertia f he olt lone estraining he earward
movement of th e cartridge case.
2-2.1 SPECIFIC REQUIREMENTS
bolts re eeded or heir nertial roperties, imple
blowback ystems re uitable nly or ow mpulse,
relatively lo w rate of fire weapons
3
T he estraining omponents f imple blowback
mechanism ar e the bolt an d driving spring. Fig. 2— 2 is a
schematic of an assembled unit. mmediate resistance to
case movement offered by he eturn pring is sually
negligible. hi s burden falls almost totally on the bolt. t
begins to move s oo n as the projectile tarts but t a
much lower acceleration o that the cartridge case is still
supported y he chamber until propellant as pressure
becomes oo ow o upture he ase. T o ealize lo w
acceleration, the bolt must be onsiderably heavier than
needed s a load-supporting component. n high impulse
guns, bolt izes ca n be ridiculously large. T he large mass,
being ubjected o he am e mpulse as that pplied to
propellant as nd rojectile, ill evelop he am e
momentum; onsequently, ts elocity nd
corresponding kinetic energy will be comparatively low.
T he lowly movingbolt confines the gun to a low rate of
fire.
2-3
A L L O W A B L E TRAVEL
T C
(A) T A N D A R D A SE
V
Although he bolt moves lowly, t till permits he
case to move. he permissible travel while ga s pressures
ar e till high enough to upture n unsupported ase is
indicated by ig . -3(A) or a standard cartridge ase.
Fig. 2-3(B) llustrates ho w modified case ca n increase
the ermissible ravel. he eometry f hamber nd
cartridge ase re lso nvolved. light aper r o
taper at all presents no problem but, for a large taper, an
axial displacement reates n ppreciable ap between
case nd hamber, hereby, xposing he ase o
deflections verging on upture. Therefore, or weapons
adaptable o imple blowback peration, hamber nd
case esign takes on special significance if bolt travel is
reasonable hile ropellant ases re ctive. or
high-powered guns, exploiting his same advantage gains
little. ow ittle ffect n ncrease n ravel as n
reducing bolts to acceptable sizes is demonstrated later.
T he riving pring ha s ne asic unction. t tores
of the of ecoiling bolt, later using this
energy to lam the bolt back into firing position and in
the rocess, ocks he iring mechanism, eloads, nd
trips he rigger o epeat he iring ycle. hat he
driving pring tores nl y om e of he nergy f the
recoiling bolt when firing semiautomatic shotguns, rifles,
and pistols s ndicated by he orward momentum not
being erceptible uring eloading whereas he ick
during firing is pronounced.
dt im e differential
T he mass of the bolt assembly includes about one-third
the spring as the equivalent mass of the spring in motion.
However , he ffect of he quivalent pring mass s
usually very mall and, for al l practical purposes, may be
neglected. fter the energy of free recoil is known, the
recoil nergy E
become available
v} (2-15)
T he verage force F epends on he fficiency of the
mechanical system
2-2.2 TIME OF CYCLE
T he ime f he iring ycle s etermined by he
impulse created by he propellant ases, an d by the bolt
and riving spring characteristics. he mpulse fFdt s
computed from the area beneath the force-time curve. It
is quated o the momentum of the bolt ssembly, i .e.,
eE,
e = efficiency of system
T he bolt ravel ust be ufficient o permit eady
cartridge oading nd ase extraction. he initial pring
force F, s based on experience nd , when easible, is
selected s our times the weight of the recoiling mass.
T he maximum pring force F
m
recoiled, is
2F -
a
(2-17)
T he spring force at an y time of recoil is
F = F
x = recoil distance at time t
At time t the energy remaining in the recoiling mass is
where s he fficiency f he pring ystem. n
inefficient ystem elps o esist ecoil by bsorbing
energy.
(2-19)
(2-2 1)
S et , = V f, he nitial elocity t im e ero, nd
integrate.
Sin"
1
F
0
Kx
yßl
This omputed ime oes not nclude he im e while
propellant ases re cting. he xclusion rovides
a simple solution without serious error. Since
M V Q = F
m
tox = L is
T he ounterrecoil ime s determined by he am e
procedure s hat or ecoil, xcept hat he ow
efficiency f prings deters apid ounterrecoil. he
energy of the counterrecoiling mass of the bolt assembly
at an y time t
cr
s
E
a
± M
b
cr
to
M
b
Fo
Cos-
1
— 2-27)
2-6
A M C P 706-260
2—2.2.3 otal Cycle Time
T he mass of the bolt ssembly and the bolt travel ar e
the ontrolling lements of a imple blowback ystem.
Large alues il l ecrease iring at e hereas he
converse s rue or mall alues. he r iving pring
re travel ar e
counterrecoil f he bolt will lways take onger han
recoil. T he time t
c
t, = t,+t
where ,- s time lapsed at the end of counterrecod until
th e bolt mechanism begins to move in recoil. ince the
firing rate is specified, t, s
60
t,
fr
be omputed y elating verage pring orces nd
acceleration o he ecoil nergy. he verage pring
force
a
Fa =
eE
r
eM ;
r
terms f ime nd cceleration, L — , \ he
recoil time becomes
During ounterrecoil, he ffectiveness f he pring
force is reduced by he inefficiency of the ystem. hi s
force is
eF „ M
Eq. 2-30
2L
4L
2
t > + tcr= r 1+f
L
(2-36)
By nowing he equired ycle time and the omputed
velocity of free recoil, he istance of bolt travel ca n be
determined from E q. 2-36. This computed distance will
be less than the actual because the ccelerations ar e not
constant hereby aving the effect of needing less time
to egotiate he istance n q . -36. n rder o
compensate or he horter ime, he olt ravel s
increased until the su m oft, an d t,, rom Eqs. 2-23 an d
2-27 equals the cycle time.
t, =t
IF F
s computed from E q. 2-30. Note hat
is onstant or ny iven roblem. ow y
th e udicious election f using q. -36 or
guidance) nd K, the pring forces ma y be computed by
iterative rocedures o hat 1) hen ubstituted nto
Eq. -37 he pecified ime s matched, nd 2) hen
into q. 2-17 o heck whether F
a
2-7
T he ctual iring ate s determined from the inal
computed cycle time.
(2-39)
2-2.3 EXAMPLE O F SIMPLE B L O W B A C K GUN
2—2.3.1 Specifications
Firing Rate: 00 rounds per minute
Interior Ballistics: ressure vs Time (Fig. 2-4)
Velocity vs Time (Fig. 2-4)
Weight of moving bolt assembly: lb
2-2.3.2 Computed Design Data
represents an impulse of
0.2
0.8
Figure 2 — 4 . Pressure-t ime Curve of Cal.45 (11.42mm) Round
2-8
AMCP 708-280
T he velocity of free recoil according to E q. 2—14 is
fFgdt 0.935x386.4
1 w 2
b 7 2 386.4
T he time of the firing cycle for 400 rpm is
f
c= $0 = .1 5 ec .
From E q. 2—36, th e approximate bolt travel is
L
=
where e = 0.40, the efficiency of system.
K .0 lb/in. s selected as practical or the irst trials.
This alue ay be evised f he bolt ravel becomes
excessive r other pecifications annot be met. rom
E q . 2—30 the average spring force
eE
r
0.40x56.3
F
-
From Eqs . 2—17 nd 2—18 the minimum an d maximum
spring forces are
yßh
057
lb-sec
2
/in.
m.
-^jm-^
104x386,4
T he time of the firing cycle for K = lb/in. is
= 0.01941 = .1393 lb-sec
7^ - a o i
= . 195 Cos- ' 0.74226 = 0 . 1 9 5 R=f = .143 sec.
(if) »'
2-9
c
* n
= 0.76923
At
V
At = t
n
. 552L.
s
= -j(F
o
F
m
c
y.oz
IITT )
v = £A v elocity t nd of each im e ncre-
ment
1
v
a
x = SA«, ase ravel uring ropellant as
period
2—2.3.4 ample Problem of Case Trave l
T he istance hat he as e s xtracted s the ro -
jectile eaves he ore s etermined y umerically
integrating the pressure-time curve of Fig. 2-4.
A
b
g
At
2—2.3.3 Case Trave l During Propel lant Ga s Period
Case while as pressures ar e active is
found y umerically ntegrating he nterior ballistics
pressure-time urve nd he velocity-time urve of the
1 2 8 . 8 F
g
At
Ac .053 n. , he as e ravel istance when he
projectile eaves the muzzle. hi s unsupported istance
of the case is still within the allowable travel illustrated
in Fig. 2—3.
A M C P 706-260
TABLE 2-1. CASE TRAVEL O F CA L 45 11.42 mm) G UN
t, At,
lb-sec in./sec in./sec in./sec in.
0 .1 0. 1 0.07 0 . 0 1 1 1 .4 1. 4 0.70 0.00007
0 .2 0. 1 0.56 0 .089 11.4 12.8 7 .10 0 . 0 0 0 7 1
0. 3 0. 1 1.73 0 .275 35.4 48 .2 30 .50 0 .00305
0 .4 0. 1 1.60 0 .255 32.8
81 .0 64.60 0.00646
0. 5 0.1 0 .88 0 . 1 4 0 18.0 99 .0 90 .00 0.00900
0. 6 0. 1 0.52 0 .083 10.7 109.7 104 .35 0.01043
0. 7 0. 1 0.36 0 .057 7. 3
117 .0 113 .35 0.01134
0.76 0.06 0 .16 0 .025 3.2 120 .2 1 1 8 . 6 0 0.01186
2 0.76 5.88 0 .935 120 .2
0.05292
Driving prings must be ompatible with operation
and ith he pace vailable or heir ssembly, wo
factors that limit their outside diameter, and assembled
and olid eights. he riving prings ust lso e
designed to meet the time an d energy requirement of the
firing ycle nd till av e he haracteristics hat re
essential or aintaining ow ynamic tresses. he
criteria or dynamic tresses av e been stablished by
Springfield Armory
analyses follow these criteria.
T he pring design data developed or the firing cycle
calculations are
F
Q
F = 9.62 lb, static spring force at end of recoil
L 2 .72 in., bolt travel
t
c
t
/0.0557\
r
\0.195
t - . 0 4 2 8 ec , im e of ecoil
(see par. 2-2.3.2)
According to the theory of surge waves in springs, the
dynamic tress ncreases nly lightly v er he tatic
stress if the following conditions exist:
1.67 "^ < .0 when 25
t
(Ref. 4)
v
2
T he mpact elocity f 0 t/sec hould ot e
exceeded, neither hould he velocity be es s than he
lower imit f ach ange, owever, he imits of the
ratio T T need not ecessarily be estricted o he wo
T
lower anges. or nstance, peeds ar e ess than 0
ft/sec, the limits ofXe ma y be shifted to the upper range
T
which varies between .3 3 nd 4.0, or even to he first
range of limits .6 7 to .0 . or speeds between 20 an d
2 5 t/sec, he imits of the ratio may be hifted to he
upper range that varies between .6 7 and 2.0.
T he urge ime, n terms of spring characteristics is
5
T =
r
According o q . 4 n Ref. 4, he dynamic orsional
stress is
mum tress or music wire s 50,000 lb/in? In Eq.
2-44,/(L<)rs the ext argest v en whole umber
larger han he value of — f this atio s not n even
whole number.
6
d 0.27 v^ DKT
d = .27 V 0.5* 1.0x0.01126 = .048i .
From E q . 2-41
T he static torsional stress 7 is
6
8fm£
nd
3
BACK
Timing the ignition so that the ne w round is firedjust
before he bolt eats gives the first part of the mpulse
created by he propellant ga s force opportunity to act as
a buffer or the returning bolt. he rest of the impulse
provides he ffort or ecoiling the bolt. he ystem
that bsorbs a portion of the mpulse in this manner is
called Advanced Primer Ignition Blowback. hi s system
has ts rtillery ounterpart n the out-of-battery firing
system, .e., he iring of he rtillery eapon being
initiated during counterrecoil but with the breechblock
closed.
By irtue f ts bility o ispose f he arly
influence of propellant ga s force on recoil, the advanced
primer gnition system is much more adaptable to high
rates of fire than the simple blowback system. Reducing
the ffectiveness of the mpulse by ifty percent alone
reduces the bolt weight y factor of tw o with a sub-
stantial increase in firing rate.
T he restraining components m ay be considered as real
and virtual; the real being the bolt and driving spring; the
virtual, the momentum of the returning bolt. ig . 2-5 is
schematic of the advanced primer ignition system. T he
firing cycle tarts with he bolt latched open by sear
an d he riving spring compressed. Releasing the ear,
frees he bolt or he pring to rive t orward. he
2-12
DRIVING, SPRING
moving bolt icks up a round from the feed mechanisms
an d ushes t nto he hamber. hortly efore he
round s eated, he iring mechanism ctivitates he
primer. T he firing mechanism is so positioned an d timed
that he as e s dequately upported when propellant
ga s pressures reach case-damaging proportions. he case
and bolt become fully eatedjust s the mpulse of the
propellant ga s force equals the momentum of the return-
in g bolt. hi s part f he mpulse s sually pproxi-
mately half the otal, thus establishingthe driving spring
characteristics.
applied propellant as orce drives the bolt earward in
recoil. During recoil, the case is extracted an d the driving
spring compressed until ll the recoil energy is absorbed
to top he ecoiling arts. f he ea r s el d n he
released position, he ycle s epeated nd iring con-
tinues automatically. iring ceases when the ea r moves
to the latched position.
PRIMER IGNITION
type performance, tart with the am e initial conditions
as or he imple blowback problem with he dded
provision that half the mpulse of the propellant ga s is
used to stop the returning bolt just as the cartridge seats.
Thus
/V
0.935
— 14 through — 39 ar e again used. ince only half
the mpulse s vailable to r ive he bolt n ecoil, ts
mass must be educed by alf n rder to etain he
120.4 in./sec velocity of free recoil. Thus the weight of
this bolt assembly is specified as 15 lb an d
sm
M
b
According o q. — 36, the pproximate bolt travel
is he am e 2.58 in.) s that or he imple blowback
gu n n he preceding problem. Again, s n he arlier
problem, he .58 in . bolt ravel does not yield totally
compatible esults nd must be modified o meet he
rate of fire of 400 rounds per minute or the ycle time
oft, 0.15 sec.
Since he nitial ynamic onditions, mpulse nd
energy of ecoil re half s much s hose of the re -
ceding problem, the pring constant must also be half in
order to have the am e bolt ravel. Eq. — 37 shows the
firing cycle time to be
= .4675 lb-sec
b
blowback
eM.
V-
- i m )
Another pproach llustrates he dvantage f
increasing the iring rate by ncorporating the advanced
primer echnique. he length of recoil in the preceding
problems wa s elected to balance the dynamics of the
problem nd s not ecessarily he deal minimum dis-
tance. uppose that he deal bolt ravel s .5 in . nd
that he ecoil orce f he imple blowback un s
acceptable. he mass of the bolt s adjusted to ui t the
requirements.
T he work W
W .
= i
F
o
F
m )
L
T he velocity v
r
-w-M
b
spring work is
b
/386.4\
W
h
42.214
g-f-y _ 386 .4 x 0 . 4 6 7 5
W
h
2-14
r
-j (MVI ) = -+(| j 9 8 8 0 2 .95 in.-lb.
T he time of firing cycle is
Mb b \
M
6
.281
y 60
The riving pring for he dvanced primer gnition
blowback gun has been assigned the following character-
istics to comply with the requirements of the firing cycle
for the simple blowback gun:
K = 0 .5 lb/in., spring constant
F
Q
F
m
= 4 .85 lb, spring force at en d of recoil
L = 2 .73 in., bolt travel
t
r
=T
c
spring
V f = V j 20 .4 in./sec, velocity of free recoil,
spring impact velocity
Select " T T = .8 . herefore, T "7T— 0.1126 sec.
When D .5 in., accordingto E q. 2 — 4 2
d .2 7 V KT .27 0 .5 0 .5 0.01125 = .038
From E q. 2-41
H = d 8x0.038 1.83 in., solid height.
T he static torsional stress, E q. 2 — 4 3 , is
8F
m
= 113,0001b/in
2
E q. 2—44 ha s the dynamic stress of
T
d
T he riving spring for he dvanced primer gnition
when the recoil force is equal to that of the simple blow-
back gun ha s the following characteristics:
K = .7271b/in. , spring constant
F
m
L = 1. 5 in., bolt travel
t
r
spring
v
f '
v
i
2-16
'c ,0203
When D .5 , accordingto E q . 2-42
d .2 7 y KT = .27 V 0 .5 x 1.727x0.00535 = . 045 in .
From Eq. 2-41
= Nd 7.3x0.045 1 .23 in., solid height.
T he static torsional stress, E q. 2 — 4 3 , is
8F
m
T
d
r
7
2-4 D E L A Y E D B L O W B A C K
Delayed blowback s the ystem that keeps the bolt
locked until he rojectile eaves he uzzle. At his
instant n unlocking mechanism, esponding o om e
influence uch s ecoil r ropellant as ressure,
releases he bolt hereby ermitting blowback o ake
effect.
Since he remendous mpulse eveloped y he
propellant ases while the projectile is in the bore is not
available or perating he bolt, he ecoiling mass
including driving, buffing, nd barrel prings — need not
be early o eavy s he wo ypes of blowback is -
cussed earlier.The smaller recoiling mass moves relatively
faster nd he at e f ir e ncreases orrespondingly.
Delayed blowback guns m ay borrow operating principles
from other types of action, e.g., the piston action of the
ga s operating un or the moving recoiling parts of the
recoil perating un . n ither ase, nly nlocking
activity s ssociated with these two types, the primary
activity involvingbolt ction still functions according to
the blowback principle. Fig. 2-6 shows a simple locking
system.
gruous with iming particularly with respect to unlock-
in g ime. f ecoil operated, distance lso becomes n
important actor. or his ype un , he barrel ust
recoil hort istance before he oving parts orce
open the bolt lock. ufficient time should elapse per-
m it he propellant as ressure to drop to evels below
the bursting ressure f he artridge ase but etain
enough intensity to blow back the bolt.
2-17
BOUT FU L L Y RECOILEr
UNLOCK ING T R A V E L
Figure 2-6. Locking System fo r De layed Blowback
T he tiffness of the prings should not be o great as
to interfere unduly with early recoil. Therefore, a system
consisting of hree prings s ustomarily sed: 1 )
barrel spring having an initial load slightly larger than the
recoiling weight to insure almost free recoil and still have
the apacity o hold he barrel in battery, 2) buffer
spring to top the ecoiling parts nd return them, nd
(3 ) bolt riving spring to ontrol bolt ctivity. Before
th e bolt s unlocked, ll moving parts ecoil as on e mass
with only the barrel spring resisting recoil but this spring
force s egligible compared to he propellant ga s force
an d ay e eglected uring ecoil. fter he olt
becomes unlocked, he barrel spring combines with the
buffer spring to arrest the recoiling barrel unit.
The unlocked bolt ontinues to be accelerated to the
rear by he mpetus of the ecaying propellant ga s pres-
sure whose only esistance no w is the force of the r iv-
in g spring, a negligible resistance until the propellant gas
pressure ecomes lmost ero. hereafter, he pring
stops he bolt nd ater loses it. Normally he barrel
unit as ompleted ounterrecoil on g before he bolt
has ully ecoiled o rovide he ime nd elative dis-
tance needed for extracting, jecting, and loading. After
the barrel unit is in battery, he bolt unit functions as a
single spring unit.
While he omplete unit s ecoiling freely an d later
while ll springs ar e operating effectively, the dynamics
of he ystem re eadily omputed y n terative
process. iven the pressure-time curve, by knowing the
size of the masses in motion, he dynamics at an y given
time re etermined y he ummations of computed
values for al l preceding increments of t ime. T he impulse
during each increment is
At = time increment
resistance offered by he driving spring. F At hould be
adjusted fter the riving spring an d ga s pressure forces
become relatively significant. During each increment, the
differential velocity is
FAt.
T he elocity f ecoil t he nd f ach ncrement
becomes
v =%_
1
2-18
AMCP 706-260
T he distance traveled by the bolt with respect to the gu n
frame during the increment is
A x
average velocity for the increment.
The total distance at the en d of each increment is
x Ax.
effective, he ehavior f he arrel nd olt nits
depend ntirely on springs. O ne uch instance involving
t
USAMC ltr, 14 Jan 1972
' £ * & &
-aiiv 3
A M C A M P H L E T M C P 706-260
ENGINEERING DESIGN
GUNS ERIES
A U T O M A T I C W E A P O N S
m
o «70
H E A D Q U A R T E R S , . S . R M Y M A T E R I E L O M M A N D E B R U A R Y 9 7 0
Ipiiir
No. 706-260
H E A D Q U A R T E R S
UNITED S T A T ES R M Y A T ER I E L O M M A N D
WASHINGTON. D . . 0315
ENGINEERING ES IGN A N D B O O K
AUTOMAT IC E A P O N S
5 February 1970
Paragraph
1-1
1-2
1-3
1-4
LIST O F I L L U S T R A T I O N S
LISTOFTABLES
PREFACE
C H A P T E R . N T R O D U C T I O N
G E N E R A L
D E F I N I T I O N S
D E S I G N P R I N C I P L E S FOR A U T O M A T I C W E A P O N S
Page
\i
viii
x
1-1
1-1
1-1
1-1
C H A P T E R 2. B L O W B A C K W E A P O N S
2-1 G E N E R A L
-1
2-2 SIMPLE B L O W B A C K -3
2—2.2.2 Counterrecoil Time -6
2-2.2.3 Total Cycle Time -7
2-2.3 E X A M P L E O F IMPLE B L O W B A C K G U N -8
2-2.3.1 Specifications
-8
2—2.3 .3 Case Travel During Propellant G as Period -10
2-2.3.4 Sample Problem of Case Travel
— 11
2-3 A D V A N C E D PRIMER I G N I T I O N B L O W B A C K -12
-12
2-3.2 A M P L E C A L C U L A T I O N S OF A D V A N C E D
PRIMER I G N I T I O N -13
2-3.2.1 Firing Rate
— 15
-17
-17
2-4.2 D Y N A M I C S O F D E L A Y E D B L O W B A C K -18
2-4.3 P R O B L E M FOR D E L A Y E D
B L O W B A C K A C T I O N -24
2-4.3.1 Specifications
2-4.3.2 Design Data -24
2-4.4 O M P U T E R ROUTINE FOR C O U N T E R R E C O I L I N G
B A R R E L D Y N A M I C S -33
2-4.5 S P R I N G S
-40
TABLE F O N T E N T S Con't.)
Paragraph ag e
2-5.2 D Y N A M I C S O F RETARDED B L O W B A C K -40
2—5.2.1 Kinematics of the Linkage
the Dynamic Analysis
— 44
2-6 R A T I N G O F B L O W B A C K W E A P O N S -47
C H A P T E R 3. R E C O I L - O P E R A T E D
3-1 G E N E R A L
-1
_i
3-3 S A M P L E P R O B L E M _LONG R E C O I L M A C H I N E G U N .. -1
3-3.1 S P E C I F I C A T I O N S _1
3-3.2 DESIGNDATA -1
_9
3-5 SAMPLE P R O B L E M _ S H O R T R E C O I L M A C H I N E G U N -9
3-5.1 S P E C I F I C A T I O N S _9
3-5.2 DESIGNDATA -9
3-6 A C C E L E R A T O R S _15
3-7 SAMPLE P R O B L E M ACCELERATOR -17
3-7.1 S P E C I F I C A T I O N S -17
3-7.2 DESIGNDATA -17
3-8 R A T I N G OF R E C O I L - O P E R A T E D G U N S -21
C H A P T E R 4. A S - O P E R A T E D W E A P O N S
4-1 GENERALREQUIREMENTS -1
-1
-1
4-3.1 M E C H A N I C S OF T H E Y S T E M _i
4—3.1 .1 G as Filling Period _g
4-3.1.2 Bolt Locking C am
4—3.1.3 C am Curve — 15
4-3.2 A M P L E P R O B L E M FOR C U T O F F E X P A N S I O N
SYSTEM
4-3.2.5 Recoil Time
— 24
4-3.3 IGITAL C O M P U T E R ROUTINE FOR C U T O F F
E X P A N S I O N
4-3.3.2.1 Bolt Unlocking During Helix Traverse -29
4-3.3.2.2 Bolt Unlocking During Parabola Traverse -29
4-3.3.2.3 ol t Unlocked, Bolt Travel ing With
Operating Rod — 31
Paragraph ag e
4-3.3.3.1 Recoil Dynamics
-37
-38
4-4.1 S A M P L E P R O B L E M -38
4-4.1.1 Specifications
4-4.1.4 Spring Design Data -45
C H A P T E R 5. REVOLVER-TYPE M A C H I N E G U N S
5-1 SINGLE B A R R E L T Y P E -1
5-1.1 P R E L I M I N A R Y D Y N A M I C S OF FIRING C Y C L E -2
5—1.1 .1 ample Problem of Preliminary iring Rate Estimate . -7
5-1.1.2 Analysis of C am Action
5-1.1.2.2 Driving Spring
-18
5_1.2 INAL E S T I M A T E OF THE C O M P L E T E FIRING C Y C L E -18
5—1.2.1 ontrol of Recoil Travel During Propellant G as Period . -20
5-1.2.2 Operating Cylinder Design
Cylinder Action -31
5 — 1.2 .4 Sample Calculation for Complete Firing Cycle -32
5-1.2.4.1 Counterrecoil Time of Recoiling Parts -33
5-1.2.4.2 igital Analyses of Barreldrum -37
5-1.2.4.3 Firing Rate Computation -39
5-2.1.2 Loading and Ejecting
— 48
5-2.2.3 Digital Computer Program for Firing Cycle -52
C H A P T E R 6. M U L T I B A R R E L M A C H I N E G U N
6-1 GENERAL
-1
6-2 B O L T O P E R A T I N G C A M D E V E L O P M E N T -1
6-2.1 CAMACTION
6-2.1.2 Definition of Symbols
Paragraph ag e
-7
6-2.3 I L L U S T R A T I V E P R O B L E M -9
6-2.3.1 am Analysis During Feed, Rotor at Constant Velocity .. -9
6-2.3.2 am Analysis During Ejection, Rotor at Constant
Velocity
6—2.3.3 C am Analysis During Rotor Acceleration — 1 2
6-2.3.4 Program for Gun .... -13
6-3 ATING O F G A S - O P E R A T E D N D E X T E R N A L L Y
POWEREDGUNS -14
C H A P T E R 7. C O M P O N E N T DESIGN
7-1 G E N E R A L
7_2 FEED M E C H A N I S M D E S I G N -1
7-2.1 M A G A Z I N E S -2
7—2.1.1 B ox Magazines
7-2.1.2.1 Flat Tape pring
-8
7-2.2 B O L T - O P E R A T E D FEED Y S T E M -9
7_2.3 ROTATING FEED M E C H A N I S M -10
7-2.3.1 Recoil-operated Feed Mechanism
7_2.4 LINKLESSFEED Y S T E M
7-2.4.2 Example Problem for Power Required -21
7 - 3 EXTRACTORS, E J E C T O R S , A ND BOLT LOCKS ~
24
7-3.2.2 Sample Problem of Ejector Dynamics -27
7-3.3 BOLTLOCKS
30
-32
7_4.1 C O M P O N E N T S , T Y P E S , A N D A C T I O N -32
7-4.1.1 Trigger Pull
-40
7_s'.2 D E S I G N R E Q U I R E M E N T S -40
7-6 M O U N T S
-
44
7_6.1 G E O M E T R Y A N D R E S O L U T I O N OF F O R C E S -44
7-6.2 S A M P L E P R O B L E M -
8
C H A P T E R 8. L U B R I C A T I O N O F M A C H I N E G U N S
3-1 ENERALCONCEPT
3-1
3-2 X A M P L E S O F L U B R I C A N T S -1
8-3 ASELUBRICANT ~
T A B L E F CONTENTS Con't.)
A P P E N D I X E S
No. Title
A-3 Flow Chart for Retarded Blowback -6
A^l Listing for Retarded Blowback Program — 9
A— 5 Flow Chart for Cutoff Expansion — 12
A-6 Listing for Cutoff Expansion Program — 15
A-7 Flow Chart for Operating Cylinder -20
A-8 Listing for Operating Cylinder Program — 22
A— 9 Flow Chart for C am and Drum Dynamics During Recoil . — 26
A — 1 0 Listing for C am and Drum Dynamics During Recoil — 30
A — 1 1 lo w Char t for C am and Drum Dynamics During
Counterrecoil
— 35
A — 1 2 isting for C am and Drum Dynamics During
Counterrecoil
— 38
A — 1 3 Flow Chart for Double Barrel Machine Gun — 43
A — 1 4 Program Listing for Double Barrel Machine Gun — 46
A-15 Flow Chart for Multibarrel Power -52
A — 1 6 Program Listing for Multibarrel Power — 59
B utomatic Control of Rounds in a Burst for
Weapon Effectiveness — 1
LIST OF LLUSTRATIONS
Fig. No. Title
2— 3 llowable Case Travel — 4
2— 4 ressure-time Curve of C al 45(11.42 mm) Round — 8
2— 5 chematic of Advanced Primer Ignition ystem — 13
2— 6 ocking System for Delayed Blowback — 18
2— 7 ressure-time Curve of 2 0 mm Round — 25
2— 8 chematic of Retarded Blowback Linkage — 40
2— 9 inematics of Retarded Blowback Linkage — 41
2 — 1 0 ynamics of Bolt and Linkage — 42
3— 1 chematic of Long Recoil ystem — 2
3— 2 chematic of Short Recoil ystem
4-3 otating Bolt Lock an d Activating C am -11
4-4 orce ystem of Bolt C am -12
4_5 ressure-time Curve of 7.62 mm Round — 18
4_6 perating Distances of Moving Parts
5— 1 chematic of Single Barrel Revolver-type Machine Gun .... — 1
5_2 wo tage Ramming _2
5— 3 orce Diagram of Recoiling Parts and lide — 3
5_4 chematic of C am Geometry — 5
5_5 am-slide Force Diagrams — 9
5— 6 ingle Barrel Drum Loading Diagram — 10
5_7 ingle Barrel Drum Dynamics
5-8 nterior Ballistics of 2 0 mm Revolver-type Gun -19
5_9 xtractor Assembly With Antidouble Feed Mechanism .... — 35
5 — 1 0 xtractor C am Assembly — 36
5 — 1 1 ocation of Basic Operations — 47
5—12 chematic of Double Barrel Drum-cam Arrangements — 47
5—13 chematic of Ammunition Feed ystem — 48
5 — 1 4 chematic of Ammunition Magazine
5_16 ouble Barrel Drum Loading Diagram — 51
5—17 ouble Barrel Drum Dynamics — 51
5 — 1 8 orce-time Curve of 2 0 mm Revolver-type Gun — 53
5 — 1 9 eometry of C am Actuating Lever
— 2
6— 2 oading Diagram of Bolt and C am During Acceleration . — 2
6_3 eed Portion of C am
— 3
6— 4 oading Diagram of Bolt and C am During Deceleration . — 7
6— 5 olt Position Diagram for Computer Analysis — 13
Fig. No. Title
age
7-1 nitial Contact of Bolt an d Cartridge Case Base _i
7-2 hamber-projectile Contact -2
7-3 ox Magazine -2
7-6 eometry of Double R ow tacking _4
7— 7 ox Magazine Follower — 4
7-8 lat ap e pring an d Loading Analogy _5
7-9 ectangular Coil Spring an d Loading Characteristics _7
7-10 chematic of Feed ystem. End View -10
7-11 eed ystem Illustrating Mechanics of Operation -11
7-12 ecoil-operated Rotating Feed Mechanism -13
7-13 eed Wheel an d Operating Lever Units -14
7-14 lectrically Operated Rotating Feed Mechanism -15
7-15 uter Drum -16
7-16 nner Drum Helix
7-18 chematic of Linkless Feed ystem -18
7-19 ath of Rounds in ingle End ystem -19
7-20 xtractors -25
7-24 liding Breech Lock _31
7-25 ipping Bolt Lock -32
7-26 iring Mechanism for Recoil Machine G un — 33
7-27 iring Mechanism for Gas-operated Machine Gun -34
hree-position Firing Mechanism
7-30 mmunition Link. al .5 0 Round
7-31 ose Fanning Flexibility. .6 2 mm Link — 42
7—32 as e Fanning Flexibility. 7.62 m m Link — 43
7-33 eometry of Base Fanning — 44
7-34 elical Flexibility. .6 2 mm Link -45
7-35 otal Folding .6 2 mm Ammunition Belt -46
7-36 artial Folding 7.62 mm Ammunition Belt -46
7—38 oading Diagram of Mount -47
Table No. Title
ag e
2- 1 as e Travel of C al 45(11.42 mm) G un -11
2-2 ecoil Travel of 20 mm Gun
2-4 nput for Delayed Blowback Program -37
2-5 ounterrecoil Dynamics of Delayed Blowback Gun -38
2-6 ymbolcode Correlation for Retarded Blowback -46
2-7 nput Data for Retarded Blowback -47
2-8 etarded Blowback Dynamics -48
3-1 ecoil Travel of 20 mm Gun
3-2 pring Design Data of Recoil-operated Guns -8
3-3 ecoil Travel of 2 0 mm Gun Equipped With Accelerator .. -17
4-1 omputed Dynamics of G as Cutoff System — 25
4-2 as Expansion Time Calculations -29
4-3 ymbolcode Correlation for Cutoff Expansion — 30
4-4 nput for Cutoff Expansion Program -31
4-5 omputed Dynamics Before G as Cutoff -32
4-6 omputed Dynamics After G as Cutoff Bolt Unlocking
During Helix Traverse
During Parabola Traverse
an d Rod Unit Recoiling After C am Action -34
4-9 omputed Dynamics. Counterrecoil Bolt Locking
During Parabola Traverse
-46
5— 1 ree Recoil Data of 2 0 mm Revolver-type Machine Gun .. — 21
5-2 reliminary Recoil Adapter Data
5-4 perating Cylinder Data for 0 .12 n.
2
2
2
2
5-9 ymbolcode Correlation for C am Dynamics -38
5_10 nput Data for Drum Dynamics During Recoil -38
5-11 nput Data for Drum Dynamics During Counterrecoil .... -39
5-12 omputed Recoil an d Operating Cylinder Data for
Orifice Area of 0.042 in .
2
-40
5-14 am and Drum Dynamics During Counterrecoil -42
5_15 ymbolcode Correlation or Double Barrel Machine Gun .. -56
5-16 nput Data for Double Barrel Machine Gun -56
5-17 ouble Barrel Machine Gun Dynamics — 59
VII
Table No. Title
Multibarrel Gun -14
Power
7-1 Power Required fo r Linkless Belt Feed System -24
7-2 Firing Pin Dynamics -40
A
recoil travel
= bore area
case nd hamber; perating ylinder
piston area
»c r
= orifice area
C
r
major xi s f lliptical am ; ength f D
short segment of rectangular coil spring
= average linear acceleration
= cceleration of chutes
d
ca m path
p
acceleration
= or : 1 acceleration of ca m roller on ca m
path
a
at
travel; ollective erm n efining ime
during polytropic expansion of ga s
=minor xi s of an elliptical cam; length of
long egment of ectangular oi l pring;
spring width
elliptical ca m
ca m
= orifice coefficient
rear support
= drum diameter
= wire diameter
operating cylinder
= differential time
= differential distance
and driving springs
J
crb
gas cutoff
= counterrecoil energy
= counterrecoil nergy f barrel t nd of
buffer action
ment
= energy of rotating parts, drum energy
= counterrecoil energy of drum
= energy of drum-slide system
= ejection energy of case
= energy of operating rod
=energy f ecoiling arts; nergy o e
absorbed by mount
spring; driving spring energy
of unlocking of bolt
slide
E = energy loss attributed to spring system
E = total energy loss caused by friction
energy loss in drum
energy loss in slide
base of natural logarithms
force; pring force t beginning of recoil
= general expression for average force; aver-
ag e riving pring orce; xial nertial
force
= buffer spring force
= operating cylinder force
force, entrance orce, maximum extractor
load to clear cartridge case
= effective force on barrel
gas force
on bolt
of recoil
:
ob
r
obs
sh
tb
spring
adapter
in g load
= initial buffer spring force
= ca m roller pin load
= average force during recoil
cartridge case or round
force
reaction of trigger spring pin
= average adapter force or time intervals
= barrel spring force at end of propellant ga s
period
pulse
to surge time
= command height
intersection
mass moment of inertia
=mass oment f nertia f drum; mass
moment of inertia of al l rotating parts
= effective mass moment of inertia of drum
= area polar moment of inertia
= pring constant, general; driving pring
constant
= buffer spring constant
springs
adapter
tion
= ratio of specific heats; radius of gyration;
bolt polar radius of gyration
= general xpression or lengths; ength of
recoil; bolt travel; length of flat spring
:
:
total peripheral length of ca m
:
travel
:
= length of round; ength of rear pintle leg
= appet travel; barrel spring operating
deflection
bending moment
= effective mass of ammunition
belt; effective mass of rotating drum
:
:
:
first bend of flat tape spring
:
:
:
curve; ormal orce on roller; number of
rounds; number of active egments in flat
spring
of links of ammunition
:
:
:
:
general erm or pace between ounds
(pitch)
:
= . critical pressure
muzzle
Pu
cartridge case
R
a
round
R,
= distance from ca m contact point o drum
axis
= roller radius; rack eactions du e to ota-
tional forces
ger reaction on sear
= mean radius of case
= distance from tipping point on ri m to C G
.ofcase
= extractor radius
= triker radius
s
a
during recoil
= utoff distance
= dwell distance
time
recoil
tion here lide ontacts as perating
unit
= travel component ue o change in veloci-
ty
torque of trigger spring
= compression time of spring
an d case
= locking lug torque
= required retainer torque
= ccelerating torque
= esisting torque
= pplied torque
= buffer time
action
contacted
= duration of propellant ga s period
=time nterval of well between ounter-
recoil an d recoil
= recoil time of bolt
= recoil time of barrel during pressure decay
after bolt unlocking
= thickness of spring
:
:
:
:
= final volume in gas equations
:
velocity f chutes; linear ejected velocity
of cartridge case
:
accelerating travel
tridge case at ejection, velocity of transfer
unit
= weight of round
= wall atio of case; weight of ga s in cylin-
der; weight of propellant charge
= weight of cartridge case; weight of empty
case
:
= total eight f propellant r propellant
ga s
ponents
= weight of projectile
weight; weight of spring
= weight of slide with 2 rounds
=weight of lide, ounds, nd as oper-
ating unit
= barrel weight
of flat spring
= width of cam
inx-direction
= bolt ravel at en d of propellant ga s period
= axial length of parabola
period; ecoil ravel f drum nd barrel
assembly
= ounterrecoiling ravel uring mpulse
= travel of recoiling parts during ca m dwell
period
= barrel travel during free recoil
= barrel travel during propellant ga s period;
after buffer engagement; recoil travel dur-
in g ca m dwell period
LIST F YMBOLS (Con't.)
peripheral length of constant slope of ca m
y
m
deflection
of rotor
y orrection factor
At time differential
Av velocity differential
Ax distance differential
of one spring segment
e
b
spring
0 = angular shear deflection
8 = ngular moment deflection
helix
P
P
2
= Poisson's ratio
= ummation
= angular velocity
P R E F A C E
This handbook s on e of a eries on Guns. t is part of a group of handbooks covering
the ngineering rinciples nd fundamental data eeded n he development of Army
materiel, which as , group) onstitutes he ngineering Design Handbook eries. hi s
handbook presents nformation on he undamental operating principles nd design of
automatic weapons nd pplies pecifically o utomatic weapons of all ypes uch as
blowback, ecoil-operated, as-operated, nd xternally owered. hese nclude ingle,
double, multibarrel, nd revolver-type machine guns and range from the imple blowback
to he ntricate M 6 1 A 1 Vulcan nd Navy 0 mm Aircraft G un Mark II M od Machine
Guns. Methods re advanced for preparing engineering design data on firing cycle, spring
design, ga s dynamics, magazines, oaders, firing pins, tc. A ll components ar e considered
except tube design which appears in another handbook, A M C P 706-252, G un Tubes.
This handbook wa s prepared by The Franklin Institute, Philadelphia, Pennsylvania, for
th e Engineering Handbook Office of Duke Universi ty, prime contractor to the U.S. Army,
and wa s under he echnical guidance nd coordination of a special subcommittee with
representation from Watervliet Arsenal, Rock Island Arsenal, an d Springfield Armory.
The Handbooks ar e readily vailable to ll elements of A M C including personnel nd
contractors having a need nd/or requirement. he Army Materiel Command policy is to
release hese ngineering esign Handbooks o ther D O D ctivities nd heir on -
tractors, nd other Government gencies n ccordance with urrent Army Regulation
70-31, dated 9 September 1966 . Procedures for acquiring these Handbooks follow:
a. ctivities within A M C nd other D O D agencies should direct their request on an
official form to :
Letterkenny Army Depot
A T T N : M X L E - A T D
Publications Distribution Branch
Chambersburg, Pennsylvania 1 7 2 0 1
b. ontractors ho av e epartment f efense ontracts hould ubmit heir
request, hrough heir ontracting officer with proper justification, o the ddress indi-
cated in par. .
c. overnment agencies other than D O D having need for the Handbooks may submit
their request irectly o the Letterkenny Army Depot, as indicated in par. above, or to :
Commanding General
Washington, D. C. 0315
Cameron Station
d. ndustries not having a Government contract (this ncludes Universities) must for-
ward their request to:
ATTN: MCRD-TV
Washington, D. C. 0315
e . ll foreign requests must be ubmitted through the Washington, D . C. Embassy to:
Office of the Assistant Chief of Staff for Intelligence
ATTN: oreign Liaison Office
Department of the Army
Washington, D. C . 0 3 1 0
All requests, ther than those riginating within theDOD, must be accompanied by a
validjustification.
Comments and suggestions on this handbook re welcome and should be addressed to
Army Research Office-Durham, Box CM , Duke Station, Durham, N. C . 27706.
xix/xx
INTRODUCTION*
This andbook resents nd iscusses rocedures
normally practiced for the design of automatic weapons,
an d explores the problems temming from the functions
of each weapon nd ts omponents. t s ntended o
assist and uide he esigner of utomatic weapons of
the un type, nd o ontain pertinent design informa-
tion and references.
1-2 GENERAL
T he purpose of the handbook s (1 ) o cquaint ne w
personnel with he many hases of utomatic weapon
design, nd 2 ) o erve s seful eference or he
experienced ngineer. t oe s ot uplicate aterial
available in other handbooks of the weapon series. Those
topics which re presented n detail in other handbooks
ar e discussed here nl y n a general sense; consequently,
the eader must depend on the referenced handbook for
the etails. nless epetitive, he ext or yclic
analyses, ime-displacement T-D) urves, hamber
design, trength equirements, prings, ams, nd rive
systems ncludes mathematical nalyses mbodying
sketches, urves, nd llustrative roblems. opics such
as ammunition characteristics, lubrication, handling and
operating features, nd advantages an d disadvantages ar e
generally escribed or e ualitatively han uantita-
tively.
weapon ffectiveness n he point ire od e — a facet
which the gu n designer ma y wish to consider.
1-3 DEFINITIONS
An automatic weapon is a self-firing gun. T o be fully
automatic, he weapon must load, fire, extract, an d eject
continuously fter the first round s loaded nd fired -
provided hat he iring mechanism s el d nlocked.
Furthermore, he utomatic weapon derives all its oper-
ating nergy rom he propellant. om e weapons av e
external power units ttached nd, lthough not uto-
matic in the strictest sense, ar e still classified as such.
There re three eneral classes of automatic weapons,
all efined ccording o heir ystem f peration,
namely: lowback, as-operated, nd ecoil-
operated'**
mechanism that uses propellant ga s pressure to force the
bolt to he ear; barrel nd receiver remaining relatively
fiied. he ressure orce is transmitted irectly by he
cartridge as e base to he bolt.
b. as-operated s the system that uses the propellant
gases hat av e een vented rom he bore o r ive
piston inked o he olt. he oving iston irst
unlocks the bolt, then drives it rearward.
c. ecoil-operated is the ystem that uses the energy
of the recoiling parts to operate the gun.
Each ystem as ariations hat ay orrow ne r
more perational eatures rom he thers. hese
variations, s well s he asic ystems, re iscussed
thoroughly n later chapters.
WEAPONS
round f mmunition, s ssentially he am e s ny
other un . ts basic ifference s having the bility o
continue iring many ounds rapidly nd automatically.
A n outer stimulus is needed nl y o tart or stop firing,
unless he atter ccurs hen mmunition upply s
exhausted. he utomatic eatures require major effort
in esign nd evelopment. he esign philosophy as
been established, then the gu n is to fire as fast as required
without tressing ny omponent o he xtent where
damage an d therefore malfunction is imminent.
An xtremely hort iring ycle eing asic, he
designer must exploit to he fullest he inherent proper-
ties of each type of automatic weapon. Generally, each
type ust eet ertain equirements n ddition o
*Prepared by Martin Regina, Franklin Institute Research
Laboratories,Philadelphia,Pennsylvania.
1-1
ments or design features are:
1 . Jte part of the vailable energy of the propellant
gases without materially affecting the ballistics.
2 . ir e ccurately t a sustained rate compatible with
the required tactics.
5. Have a mechanism that is:
a. imple to operate
6. Have positive action for feeding, extracting, ject-
ing.
ments ut o egree ormally imited y ype f
weapon. onflicting equirements re resolved by om -
promise.
1-2
C H A P T E R 2
BLOWBACK WEAPONS
Controlling he esponse of the cartridge case to the
propellant as ressure s the asic esign riterion f
blowback eapons. he ase esponds by ending o
move earward nder he nfluence of the xial orce
generated by he as pressure on ts base. Meanwhile,
because of this same pressure, the case dilates to press on
th e nner wall of the hamber. he axial force tends to
push he bolt earward, opposed only by he esistance
offered by he bolt nertia nd the rictional resistance
between ase and chamber wall. T h question no w arises
as to which response redominates, he mpending axial
motion r he rictional esistance nhibiting his
motion.
typical ressure-time urve f ound of ammunition.
3U
45
40
a.
CC
2-1
For implicity, ssume nity or bore re a nd bolt
weight. According o ig. — 1, he maximum pressure
of 5,000 si evelops n . 0005 ec. gain or
simplicity, assume that he ressure varies linearly rom
t o . 0005 ec. he ressure/» t ny im e
during he nterval
'-(jra)'- ''»*'
(2-1)
T he corresponding force F driving the cartridge case an d
bolt rearward is
where A
but,by assumption, A
b
but
J t
Integration of Eq. — 7 yields
(2-8)
2
0 .
Assume hat he imiting learance etween ase nd
chamber s qual o he ase dilation s t eaches the
ultimate trength, and assume further that the artridge
case as nominal outside diameter of .5 n. , wall
thickness of 0.05 n. , an d an ultimate trength of 50,000
psi. hen, ccording o he hin-walled ressure vessel
formula, he ressure t hich ailure mpends nd
which presses the ase firmly against the chamber wall is
Pu
o
t
t
r
50,000x0.05
t
c
a
t
, ensile tress
From q. 2 — 1 , s he ime lapsed o each his
pressure.
Pu
t
sec (2-10)
From q. — 8, s the distance that the as e and bolt
travel during this time, .e., when only the inertia of the
system is considered.
15
prevail, he artridge as e carcely oves efore
frictional esistance egins o ake ffect. Motion will
continue until E q. 2—11 is satisfied.
A
b
where
case an d chamber
Pi interface pressure of case an d chamber
ß coefficient of friction
an approximate interface pressure p
t
by quating the inside deflection of the chamber, due to
this ressure, o he utside deflection of the cartridge
case, ue o both interface and propellant as pressure,
when both case an d chamber ar considered cylindrical.
Solve for the interface pressure.
2p
W . wall ratio of case
v Poisson's atio assumed o be qual for
both materials)
unsupported artridge cases to the limit of their strength
are easonably lose o he difference in propellant as
pressure an d computed interface pressure. Thus
Pu * P-Pi
exceeds ase ecovery fter as ressures ubside;
otherwise, nterference evelops, i.e., lamping the ase
to he chamber wall an d rendering extraction difficult*.
2-2 SIMPLE B L O W B A C K
Simple lowback s he ystem herein ll he
operating nergy s erived rom blowback with he
inertia f he olt lone estraining he earward
movement of th e cartridge case.
2-2.1 SPECIFIC REQUIREMENTS
bolts re eeded or heir nertial roperties, imple
blowback ystems re uitable nly or ow mpulse,
relatively lo w rate of fire weapons
3
T he estraining omponents f imple blowback
mechanism ar e the bolt an d driving spring. Fig. 2— 2 is a
schematic of an assembled unit. mmediate resistance to
case movement offered by he eturn pring is sually
negligible. hi s burden falls almost totally on the bolt. t
begins to move s oo n as the projectile tarts but t a
much lower acceleration o that the cartridge case is still
supported y he chamber until propellant as pressure
becomes oo ow o upture he ase. T o ealize lo w
acceleration, the bolt must be onsiderably heavier than
needed s a load-supporting component. n high impulse
guns, bolt izes ca n be ridiculously large. T he large mass,
being ubjected o he am e mpulse as that pplied to
propellant as nd rojectile, ill evelop he am e
momentum; onsequently, ts elocity nd
corresponding kinetic energy will be comparatively low.
T he lowly movingbolt confines the gun to a low rate of
fire.
2-3
A L L O W A B L E TRAVEL
T C
(A) T A N D A R D A SE
V
Although he bolt moves lowly, t till permits he
case to move. he permissible travel while ga s pressures
ar e till high enough to upture n unsupported ase is
indicated by ig . -3(A) or a standard cartridge ase.
Fig. 2-3(B) llustrates ho w modified case ca n increase
the ermissible ravel. he eometry f hamber nd
cartridge ase re lso nvolved. light aper r o
taper at all presents no problem but, for a large taper, an
axial displacement reates n ppreciable ap between
case nd hamber, hereby, xposing he ase o
deflections verging on upture. Therefore, or weapons
adaptable o imple blowback peration, hamber nd
case esign takes on special significance if bolt travel is
reasonable hile ropellant ases re ctive. or
high-powered guns, exploiting his same advantage gains
little. ow ittle ffect n ncrease n ravel as n
reducing bolts to acceptable sizes is demonstrated later.
T he riving pring ha s ne asic unction. t tores
of the of ecoiling bolt, later using this
energy to lam the bolt back into firing position and in
the rocess, ocks he iring mechanism, eloads, nd
trips he rigger o epeat he iring ycle. hat he
driving pring tores nl y om e of he nergy f the
recoiling bolt when firing semiautomatic shotguns, rifles,
and pistols s ndicated by he orward momentum not
being erceptible uring eloading whereas he ick
during firing is pronounced.
dt im e differential
T he mass of the bolt assembly includes about one-third
the spring as the equivalent mass of the spring in motion.
However , he ffect of he quivalent pring mass s
usually very mall and, for al l practical purposes, may be
neglected. fter the energy of free recoil is known, the
recoil nergy E
become available
v} (2-15)
T he verage force F epends on he fficiency of the
mechanical system
2-2.2 TIME OF CYCLE
T he ime f he iring ycle s etermined by he
impulse created by he propellant ases, an d by the bolt
and riving spring characteristics. he mpulse fFdt s
computed from the area beneath the force-time curve. It
is quated o the momentum of the bolt ssembly, i .e.,
eE,
e = efficiency of system
T he bolt ravel ust be ufficient o permit eady
cartridge oading nd ase extraction. he initial pring
force F, s based on experience nd , when easible, is
selected s our times the weight of the recoiling mass.
T he maximum pring force F
m
recoiled, is
2F -
a
(2-17)
T he spring force at an y time of recoil is
F = F
x = recoil distance at time t
At time t the energy remaining in the recoiling mass is
where s he fficiency f he pring ystem. n
inefficient ystem elps o esist ecoil by bsorbing
energy.
(2-19)
(2-2 1)
S et , = V f, he nitial elocity t im e ero, nd
integrate.
Sin"
1
F
0
Kx
yßl
This omputed ime oes not nclude he im e while
propellant ases re cting. he xclusion rovides
a simple solution without serious error. Since
M V Q = F
m
tox = L is
T he ounterrecoil ime s determined by he am e
procedure s hat or ecoil, xcept hat he ow
efficiency f prings deters apid ounterrecoil. he
energy of the counterrecoiling mass of the bolt assembly
at an y time t
cr
s
E
a
± M
b
cr
to
M
b
Fo
Cos-
1
— 2-27)
2-6
A M C P 706-260
2—2.2.3 otal Cycle Time
T he mass of the bolt ssembly and the bolt travel ar e
the ontrolling lements of a imple blowback ystem.
Large alues il l ecrease iring at e hereas he
converse s rue or mall alues. he r iving pring
re travel ar e
counterrecoil f he bolt will lways take onger han
recoil. T he time t
c
t, = t,+t
where ,- s time lapsed at the end of counterrecod until
th e bolt mechanism begins to move in recoil. ince the
firing rate is specified, t, s
60
t,
fr
be omputed y elating verage pring orces nd
acceleration o he ecoil nergy. he verage pring
force
a
Fa =
eE
r
eM ;
r
terms f ime nd cceleration, L — , \ he
recoil time becomes
During ounterrecoil, he ffectiveness f he pring
force is reduced by he inefficiency of the ystem. hi s
force is
eF „ M
Eq. 2-30
2L
4L
2
t > + tcr= r 1+f
L
(2-36)
By nowing he equired ycle time and the omputed
velocity of free recoil, he istance of bolt travel ca n be
determined from E q. 2-36. This computed distance will
be less than the actual because the ccelerations ar e not
constant hereby aving the effect of needing less time
to egotiate he istance n q . -36. n rder o
compensate or he horter ime, he olt ravel s
increased until the su m oft, an d t,, rom Eqs. 2-23 an d
2-27 equals the cycle time.
t, =t
IF F
s computed from E q. 2-30. Note hat
is onstant or ny iven roblem. ow y
th e udicious election f using q. -36 or
guidance) nd K, the pring forces ma y be computed by
iterative rocedures o hat 1) hen ubstituted nto
Eq. -37 he pecified ime s matched, nd 2) hen
into q. 2-17 o heck whether F
a
2-7
T he ctual iring ate s determined from the inal
computed cycle time.
(2-39)
2-2.3 EXAMPLE O F SIMPLE B L O W B A C K GUN
2—2.3.1 Specifications
Firing Rate: 00 rounds per minute
Interior Ballistics: ressure vs Time (Fig. 2-4)
Velocity vs Time (Fig. 2-4)
Weight of moving bolt assembly: lb
2-2.3.2 Computed Design Data
represents an impulse of
0.2
0.8
Figure 2 — 4 . Pressure-t ime Curve of Cal.45 (11.42mm) Round
2-8
AMCP 708-280
T he velocity of free recoil according to E q. 2—14 is
fFgdt 0.935x386.4
1 w 2
b 7 2 386.4
T he time of the firing cycle for 400 rpm is
f
c= $0 = .1 5 ec .
From E q. 2—36, th e approximate bolt travel is
L
=
where e = 0.40, the efficiency of system.
K .0 lb/in. s selected as practical or the irst trials.
This alue ay be evised f he bolt ravel becomes
excessive r other pecifications annot be met. rom
E q . 2—30 the average spring force
eE
r
0.40x56.3
F
-
From Eqs . 2—17 nd 2—18 the minimum an d maximum
spring forces are
yßh
057
lb-sec
2
/in.
m.
-^jm-^
104x386,4
T he time of the firing cycle for K = lb/in. is
= 0.01941 = .1393 lb-sec
7^ - a o i
= . 195 Cos- ' 0.74226 = 0 . 1 9 5 R=f = .143 sec.
(if) »'
2-9
c
* n
= 0.76923
At
V
At = t
n
. 552L.
s
= -j(F
o
F
m
c
y.oz
IITT )
v = £A v elocity t nd of each im e ncre-
ment
1
v
a
x = SA«, ase ravel uring ropellant as
period
2—2.3.4 ample Problem of Case Trave l
T he istance hat he as e s xtracted s the ro -
jectile eaves he ore s etermined y umerically
integrating the pressure-time curve of Fig. 2-4.
A
b
g
At
2—2.3.3 Case Trave l During Propel lant Ga s Period
Case while as pressures ar e active is
found y umerically ntegrating he nterior ballistics
pressure-time urve nd he velocity-time urve of the
1 2 8 . 8 F
g
At
Ac .053 n. , he as e ravel istance when he
projectile eaves the muzzle. hi s unsupported istance
of the case is still within the allowable travel illustrated
in Fig. 2—3.
A M C P 706-260
TABLE 2-1. CASE TRAVEL O F CA L 45 11.42 mm) G UN
t, At,
lb-sec in./sec in./sec in./sec in.
0 .1 0. 1 0.07 0 . 0 1 1 1 .4 1. 4 0.70 0.00007
0 .2 0. 1 0.56 0 .089 11.4 12.8 7 .10 0 . 0 0 0 7 1
0. 3 0. 1 1.73 0 .275 35.4 48 .2 30 .50 0 .00305
0 .4 0. 1 1.60 0 .255 32.8
81 .0 64.60 0.00646
0. 5 0.1 0 .88 0 . 1 4 0 18.0 99 .0 90 .00 0.00900
0. 6 0. 1 0.52 0 .083 10.7 109.7 104 .35 0.01043
0. 7 0. 1 0.36 0 .057 7. 3
117 .0 113 .35 0.01134
0.76 0.06 0 .16 0 .025 3.2 120 .2 1 1 8 . 6 0 0.01186
2 0.76 5.88 0 .935 120 .2
0.05292
Driving prings must be ompatible with operation
and ith he pace vailable or heir ssembly, wo
factors that limit their outside diameter, and assembled
and olid eights. he riving prings ust lso e
designed to meet the time an d energy requirement of the
firing ycle nd till av e he haracteristics hat re
essential or aintaining ow ynamic tresses. he
criteria or dynamic tresses av e been stablished by
Springfield Armory
analyses follow these criteria.
T he pring design data developed or the firing cycle
calculations are
F
Q
F = 9.62 lb, static spring force at end of recoil
L 2 .72 in., bolt travel
t
c
t
/0.0557\
r
\0.195
t - . 0 4 2 8 ec , im e of ecoil
(see par. 2-2.3.2)
According to the theory of surge waves in springs, the
dynamic tress ncreases nly lightly v er he tatic
stress if the following conditions exist:
1.67 "^ < .0 when 25
t
(Ref. 4)
v
2
T he mpact elocity f 0 t/sec hould ot e
exceeded, neither hould he velocity be es s than he
lower imit f ach ange, owever, he imits of the
ratio T T need not ecessarily be estricted o he wo
T
lower anges. or nstance, peeds ar e ess than 0
ft/sec, the limits ofXe ma y be shifted to the upper range
T
which varies between .3 3 nd 4.0, or even to he first
range of limits .6 7 to .0 . or speeds between 20 an d
2 5 t/sec, he imits of the ratio may be hifted to he
upper range that varies between .6 7 and 2.0.
T he urge ime, n terms of spring characteristics is
5
T =
r
According o q . 4 n Ref. 4, he dynamic orsional
stress is
mum tress or music wire s 50,000 lb/in? In Eq.
2-44,/(L<)rs the ext argest v en whole umber
larger han he value of — f this atio s not n even
whole number.
6
d 0.27 v^ DKT
d = .27 V 0.5* 1.0x0.01126 = .048i .
From E q . 2-41
T he static torsional stress 7 is
6
8fm£
nd
3
BACK
Timing the ignition so that the ne w round is firedjust
before he bolt eats gives the first part of the mpulse
created by he propellant ga s force opportunity to act as
a buffer or the returning bolt. he rest of the impulse
provides he ffort or ecoiling the bolt. he ystem
that bsorbs a portion of the mpulse in this manner is
called Advanced Primer Ignition Blowback. hi s system
has ts rtillery ounterpart n the out-of-battery firing
system, .e., he iring of he rtillery eapon being
initiated during counterrecoil but with the breechblock
closed.
By irtue f ts bility o ispose f he arly
influence of propellant ga s force on recoil, the advanced
primer gnition system is much more adaptable to high
rates of fire than the simple blowback system. Reducing
the ffectiveness of the mpulse by ifty percent alone
reduces the bolt weight y factor of tw o with a sub-
stantial increase in firing rate.
T he restraining components m ay be considered as real
and virtual; the real being the bolt and driving spring; the
virtual, the momentum of the returning bolt. ig . 2-5 is
schematic of the advanced primer ignition system. T he
firing cycle tarts with he bolt latched open by sear
an d he riving spring compressed. Releasing the ear,
frees he bolt or he pring to rive t orward. he
2-12
DRIVING, SPRING
moving bolt icks up a round from the feed mechanisms
an d ushes t nto he hamber. hortly efore he
round s eated, he iring mechanism ctivitates he
primer. T he firing mechanism is so positioned an d timed
that he as e s dequately upported when propellant
ga s pressures reach case-damaging proportions. he case
and bolt become fully eatedjust s the mpulse of the
propellant ga s force equals the momentum of the return-
in g bolt. hi s part f he mpulse s sually pproxi-
mately half the otal, thus establishingthe driving spring
characteristics.
applied propellant as orce drives the bolt earward in
recoil. During recoil, the case is extracted an d the driving
spring compressed until ll the recoil energy is absorbed
to top he ecoiling arts. f he ea r s el d n he
released position, he ycle s epeated nd iring con-
tinues automatically. iring ceases when the ea r moves
to the latched position.
PRIMER IGNITION
type performance, tart with the am e initial conditions
as or he imple blowback problem with he dded
provision that half the mpulse of the propellant ga s is
used to stop the returning bolt just as the cartridge seats.
Thus
/V
0.935
— 14 through — 39 ar e again used. ince only half
the mpulse s vailable to r ive he bolt n ecoil, ts
mass must be educed by alf n rder to etain he
120.4 in./sec velocity of free recoil. Thus the weight of
this bolt assembly is specified as 15 lb an d
sm
M
b
According o q. — 36, the pproximate bolt travel
is he am e 2.58 in.) s that or he imple blowback
gu n n he preceding problem. Again, s n he arlier
problem, he .58 in . bolt ravel does not yield totally
compatible esults nd must be modified o meet he
rate of fire of 400 rounds per minute or the ycle time
oft, 0.15 sec.
Since he nitial ynamic onditions, mpulse nd
energy of ecoil re half s much s hose of the re -
ceding problem, the pring constant must also be half in
order to have the am e bolt ravel. Eq. — 37 shows the
firing cycle time to be
= .4675 lb-sec
b
blowback
eM.
V-
- i m )
Another pproach llustrates he dvantage f
increasing the iring rate by ncorporating the advanced
primer echnique. he length of recoil in the preceding
problems wa s elected to balance the dynamics of the
problem nd s not ecessarily he deal minimum dis-
tance. uppose that he deal bolt ravel s .5 in . nd
that he ecoil orce f he imple blowback un s
acceptable. he mass of the bolt s adjusted to ui t the
requirements.
T he work W
W .
= i
F
o
F
m )
L
T he velocity v
r
-w-M
b
spring work is
b
/386.4\
W
h
42.214
g-f-y _ 386 .4 x 0 . 4 6 7 5
W
h
2-14
r
-j (MVI ) = -+(| j 9 8 8 0 2 .95 in.-lb.
T he time of firing cycle is
Mb b \
M
6
.281
y 60
The riving pring for he dvanced primer gnition
blowback gun has been assigned the following character-
istics to comply with the requirements of the firing cycle
for the simple blowback gun:
K = 0 .5 lb/in., spring constant
F
Q
F
m
= 4 .85 lb, spring force at en d of recoil
L = 2 .73 in., bolt travel
t
r
=T
c
spring
V f = V j 20 .4 in./sec, velocity of free recoil,
spring impact velocity
Select " T T = .8 . herefore, T "7T— 0.1126 sec.
When D .5 in., accordingto E q. 2 — 4 2
d .2 7 V KT .27 0 .5 0 .5 0.01125 = .038
From E q. 2-41
H = d 8x0.038 1.83 in., solid height.
T he static torsional stress, E q. 2 — 4 3 , is
8F
m
= 113,0001b/in
2
E q. 2—44 ha s the dynamic stress of
T
d
T he riving spring for he dvanced primer gnition
when the recoil force is equal to that of the simple blow-
back gun ha s the following characteristics:
K = .7271b/in. , spring constant
F
m
L = 1. 5 in., bolt travel
t
r
spring
v
f '
v
i
2-16
'c ,0203
When D .5 , accordingto E q . 2-42
d .2 7 y KT = .27 V 0 .5 x 1.727x0.00535 = . 045 in .
From Eq. 2-41
= Nd 7.3x0.045 1 .23 in., solid height.
T he static torsional stress, E q. 2 — 4 3 , is
8F
m
T
d
r
7
2-4 D E L A Y E D B L O W B A C K
Delayed blowback s the ystem that keeps the bolt
locked until he rojectile eaves he uzzle. At his
instant n unlocking mechanism, esponding o om e
influence uch s ecoil r ropellant as ressure,
releases he bolt hereby ermitting blowback o ake
effect.
Since he remendous mpulse eveloped y he
propellant ases while the projectile is in the bore is not
available or perating he bolt, he ecoiling mass
including driving, buffing, nd barrel prings — need not
be early o eavy s he wo ypes of blowback is -
cussed earlier.The smaller recoiling mass moves relatively
faster nd he at e f ir e ncreases orrespondingly.
Delayed blowback guns m ay borrow operating principles
from other types of action, e.g., the piston action of the
ga s operating un or the moving recoiling parts of the
recoil perating un . n ither ase, nly nlocking
activity s ssociated with these two types, the primary
activity involvingbolt ction still functions according to
the blowback principle. Fig. 2-6 shows a simple locking
system.
gruous with iming particularly with respect to unlock-
in g ime. f ecoil operated, distance lso becomes n
important actor. or his ype un , he barrel ust
recoil hort istance before he oving parts orce
open the bolt lock. ufficient time should elapse per-
m it he propellant as ressure to drop to evels below
the bursting ressure f he artridge ase but etain
enough intensity to blow back the bolt.
2-17
BOUT FU L L Y RECOILEr
UNLOCK ING T R A V E L
Figure 2-6. Locking System fo r De layed Blowback
T he tiffness of the prings should not be o great as
to interfere unduly with early recoil. Therefore, a system
consisting of hree prings s ustomarily sed: 1 )
barrel spring having an initial load slightly larger than the
recoiling weight to insure almost free recoil and still have
the apacity o hold he barrel in battery, 2) buffer
spring to top the ecoiling parts nd return them, nd
(3 ) bolt riving spring to ontrol bolt ctivity. Before
th e bolt s unlocked, ll moving parts ecoil as on e mass
with only the barrel spring resisting recoil but this spring
force s egligible compared to he propellant ga s force
an d ay e eglected uring ecoil. fter he olt
becomes unlocked, he barrel spring combines with the
buffer spring to arrest the recoiling barrel unit.
The unlocked bolt ontinues to be accelerated to the
rear by he mpetus of the ecaying propellant ga s pres-
sure whose only esistance no w is the force of the r iv-
in g spring, a negligible resistance until the propellant gas
pressure ecomes lmost ero. hereafter, he pring
stops he bolt nd ater loses it. Normally he barrel
unit as ompleted ounterrecoil on g before he bolt
has ully ecoiled o rovide he ime nd elative dis-
tance needed for extracting, jecting, and loading. After
the barrel unit is in battery, he bolt unit functions as a
single spring unit.
While he omplete unit s ecoiling freely an d later
while ll springs ar e operating effectively, the dynamics
of he ystem re eadily omputed y n terative
process. iven the pressure-time curve, by knowing the
size of the masses in motion, he dynamics at an y given
time re etermined y he ummations of computed
values for al l preceding increments of t ime. T he impulse
during each increment is
At = time increment
resistance offered by he driving spring. F At hould be
adjusted fter the riving spring an d ga s pressure forces
become relatively significant. During each increment, the
differential velocity is
FAt.
T he elocity f ecoil t he nd f ach ncrement
becomes
v =%_
1
2-18
AMCP 706-260
T he distance traveled by the bolt with respect to the gu n
frame during the increment is
A x
average velocity for the increment.
The total distance at the en d of each increment is
x Ax.
effective, he ehavior f he arrel nd olt nits
depend ntirely on springs. O ne uch instance involving
t