Airgun Ammunition Project
Team Members
Bryan LaMora
Joe Ouellette
Zach Rohlfs
Team 07F
Task: Provide an economical material to replace the current lead pellet.
Reason: Due to health concerns lead pellets will
eventually be discontinued.
Project Definition
Specifications
Pellet Size:
-.177 cal.
-.176 +.003/-.0005
-.4 to 10.5 grain
-.195” to .260” (ASTM F 590)
-Any Shape
Specifications
Requirements:
-minimum 24 lb shot force
-Non-Toxic
-100 ft/s to 1200 ft/s velocity range
--30 to 100 deg F operating temp.
-Immune to black oxide oils
-Remain intact after impact
-$.10 to $.80 per 100 pellet cost
-.835” @ 25yd Shot Group
Ideas & Evaluation
- All steel pellet
- Composite pellet
- BB encased in plastic
- Steel cylinder encased in plastic
- Plastic and Iron filings mix
Design Obstacles
-Metal and plastic composite
-Steel core
-Plastic exterior
Design Obstacles
•Sacrificed aerodynamics to increase weight
•Keeping the manufacturing process as simple as possible
Plastics Research
Requirements:
-Dense
-Impact resistant
-Fairly high melting point
-Inexpensive
-Easily molded or thermoformed
Plastic Body Material
- Criteria- Impact resistant at
low temperature- High density- Low cost- Easily injection
molded
- Material- Polypropylene- Polystyrene- PVC- ABS- Acrylic- Polyester- Nylon- Polyethylene- Fluoropolymers- Polycarbonate
Inner Material
- Criteria- Coefficient of
restitution- Density- Cost
- Materials- Aluminum - Nickel - Tin- Steel- Brass- Copper
Bounce Back Effect
- Lead: 55 Feet- Copper: 77 Feet- Brass: 105 Feet- Steel: 314 Feet
Bounce Back Results
Worst Case scenario coefficient of restitution: .22
Coefficient of restitution from tested : .106
Coefficient of restitution of lead: .16
Pellet Flight Characteristics
Will the velocities be approximately equal?
Is the Cd, coefficient of drag constant?
How do we determine the coefficient of drag?
What does this all mean?
Calculating Drag
AV
FC dd
2
21
Cd is the coefficient of
drag Fd is the force of drag is the density of the
fluid A is the cross-
sectional area. m is the mass of the
pellet ad is the acceleration
of drag V is the velocity of the
pellet at a given time, t
dd amF
dt
dVad
dx
dvVad
Fluent and approximations
Experimental data is not needed.
Small geometries need to be scaled by Reynolds numbers.
Two dimensional approximations differ from three dimensional.
Results and Their meaning
Cd~0.4 for hand calculations on the old pellet.
Cd~0.47 for the old pellet by Fluent using a two dimensional model.
Cd~0.56 for the new pellet by Fluent using a two dimensional model.
The velocity of the new pellet will degrade faster.
A) Pressure is constant through barrel.
B) Temperature decrease due to pressure change of gas is neglected.
C) Temperature is constant.
D) Force of gravity is negligible on pellet.
Calculation Assumptions
Pellet and Barrel
19.5”
.177”24 psi
Flow
Barrel: Brass 330
Rifling: 1 Twist in 14” Right Hand Lead
6 Lands .045” wide
Force due to Pressure
AC = Contact Area
CL = Contact Length
w = Width of Contact Area
FP = Force due to Pressure
P = Air Pressure in chamber
2.00553inC
A
)02(.277. ininCA
WLCCA
.277inLC
)6(045. inLC
.133lbPF
)200553(.2
24 ininlb
PF
CPAPF
Heat Generated by Friction
.0531lbf
F
)133)(.4(. lbfF
PFkfF
LB = Barrel Length
Wf = Work Due to Friction
FP = Force due to Pressure
DH = Change in Heat
lb.0863ftf
W
)121)(5.19)(0531(.inftinlb
fW
BLfF
fW
lb.0863ftΔΗ
f
W
Temperature Change
)( PCMwt = Material Weight
DH = Change in Heat
CP = Heat Capacity
DT = Change of Temp
Pellet Weight
Lead = .512g
Plastic = .0418g
Barrel weight
Brass 330 = 185.07g
TLead Pellet = 1.77 C
TPlastic Pellet = 1.49 C
TBarrel = .0017 C
)(
))((
wtMPC
wtMPC
Wk Mon Tues Wed Thur FriMarch1 10-14 First Day Back
2 17-21 Quarter Time Line update Empire update
3 24-28April 4 31-04 <-------------------------Tooling Setup---------------------------> Crosman Update Meeting
5 07-11 <---------------------------------------------Machining of f irst 7 pellets-------------------------------------------------------><--------Testing #1--------->6 14-18 <---------------------------------------------Machining of 40 new prototypes------------------------------------------------>
7 21-25 <--------Testing #2--------->May 8 28-02 <----------------------------------Technical paper edit------------------------------------------>Tech paper to Advisor for review .
9 05-09 <-----------Technical paper f inal edit--------------> Technical paper Turn in. Set up test f iring Pellet Firing Demonstration
10 12-16 <------------------------------Creation: poster/presentation-----------------------------> Deliverables w rap up Final Presentation
Prototyping & Testing Schedule
Conclusions
The new Pellet met the following criteria: Functions in a .177 cal Air Rifle. Between 4 and 10 grains in weight. .255 in length Operates in a velocity range of 100 to 1200
ft/sec. Nontoxic and resistant to black oxide. Low Bounce back.
Conclusions
The new Pellet fell short in the following areas: Utilize rifling in barrel:
Plastic did not conform to the rifling of the barrel.Under-sizing of pellet “skirt” will help pellet follow
rifling.
Accuracy:The lack of spin of the pellet out of the barrel.
Intact after impact:Prototype was hand machined, plastic did not “lock”
core into pellet.
Questions?