influence of particle size and temperature on the burning

Defence Research and Development Canada External Literature (P) DRDC-RDDC-2021-P061 March 2021

CAN UNCLASSIFIED

CAN UNCLASSIFIED

Influence of Particle Size and Temperature on the Burning Rate of Small Caliber Ball Powder

John Ritter Catalin-Florin Petre Pascal Béland Charles Nicole DRDC – Valcartier Research Centre Propellants, Explosives, Pyrotechnics Volume 46, pp. 1–9 Date of Publication from External Publisher: February 2021 Terms of Release: This document is approved for public release.

The body of this CAN UNCLASSIFIED document does not contain the required security banners according to DND security standards. However, it must be treated as CAN UNCLASSIFIED and protected appropriately based on the terms and conditions specified on the covering page.

Template in use: EO Publishing App for CR-EL Eng 2019-01-03-v1.dotm

© Her Majesty the Queen in Right of Canada (Department of National Defence), 2021

© Sa Majesté la Reine en droit du Canada (Ministère de la Défense nationale), 2021

CAN UNCLASSIFIED

CAN UNCLASSIFIED

IMPORTANT INFORMATIVE STATEMENTS Disclaimer: This document is not published by the Editorial Office of Defence Research and Development Canada, an agency of the Department of National Defence of Canada but is to be catalogued in the Canadian Defence Information System (CANDIS), the national repository for Defence S&T documents. Her Majesty the Queen in Right of Canada (Department of National Defence) makes no representations or warranties, expressed or implied, of any kind whatsoever, and assumes no liability for the accuracy, reliability, completeness, currency or usefulness of any information, product, process or material included in this document. Nothing in this document should be interpreted as an endorsement for the specific use of any tool, technique or process examined in it. Any reliance on, or use of, any information, product, process or material included in this document is at the sole risk of the person so using it or relying on it. Canada does not assume any liability in respect of any damages or losses arising out of or in connection with the use of, or reliance on, any information, product, process or material included in this document.

This document was reviewed for Controlled Goods by Defence Research and Development Canada using the Schedule to the Defence Production Act.

DOI: 10.1002/prep.202000289

Influence of Particle Size and Temperature on the BurningRate of Small Caliber Ball PowderJohn J. Ritter,*[a] Catalin-Florin Petre,[b] Pascal Beland,[b] and Charles Nicole[b]

Abstract: The performance of a small-caliber propellant isinfluenced by many factors. Foremost is the chemical com-position, however, other factors such as the physical prop-erties of the propellant, the weapon system, and the oper-ating conditions can also greatly influence the performanceof a propellant. In this study, researchers investigated theinfluence of particle size and temperature on the perform-ance of small caliber, ball powder propellant. Particle size isimportant as it provides the initial surface area available fora propellant to begin the deflagration process. The geome-try of the grain will dictate how the deflagration pro-

gresses: progressively, regressively, or neutral. The initialtemperature of the propellant also has a direct influence onpropellant performance. Evaluations were conducted in aconstant volume, a temperature-controlled closed vessel toobtain pressure-time data for the various experiments. Thedata coupled with the propellant thermochemical proper-ties were used to calculate the burning rate coefficient (β)and pressure exponent (α) of the propellant. Dynamic viva-city, relative force, and relative quickness values are also re-ported.

Keywords: Propellant · Burning Rate · Closed Bomb · Dynamic Vivacity · Deflagration

1 Introduction

Small caliber ammunition (.50 cal and smaller) consists ofonly a few, relatively simple parts. The major componentsare the case, primer, propellant, and projectile. The casesimply packages everything together and interfaces withthe weapon. The primer contains a primary explosive thatinitiates the interior ballistic event by generating high-pres-sure gases and hot particles upon being struck by the firingpin. The primer products interact with the propellant tocommence the deflagration process and thus generate thehigh-pressure gases necessary to propel the projectiledown the bore of the weapon and out of the muzzle. Pro-pellants can vary greatly dependent on the weapon system.In small caliber weapons, the propellant is typically a loose,granular ball powder, nominally considered spherical. Thepropellant ingredients can vary as well, but typically, theyare comprised of nitrocellulose (NC), and may or may notcontain nitroglycerine (NG). These are referred to as singlebased and double based propellants, respectively. Otherminor ingredients can be added to reduce flash, smoke,prevent aging, or aid in production. Finally, a deterrent canbe incorporated into the propellant grain. The deterrent isdesigned to control (inhibit) the initial burning rate of thepropellant grain. The deterrent is added via a chemicalprocess in which a non-energetic layer is soaked into thegrain. The chemical composition of the deterrent as well asits depth profile will determine what effects it has on theburning characteristics of the propellant grain. In this man-ner, a propellant pressure profile can be obtained to max-imize the performance of a particular weapon system.

The propellant is the primary driver that determinesweapon consistency. Therefore, a propellant manufacturermust produce propellant grains that perform as con-sistently as possible. If this is achieved, then consistentshot-to-shot performance can be realized. Deviations thatcan contribute to propellant performance variability includegrain mass, size, or chemical composition. Loading a car-tridge is a straightforward process therefore the mass ofpropellant loaded into a cartridge is easily controlled andverified. A propellant is manufactured in large batches;therefore, the grain size and chemical composition, as wellas deterrent profile, will have distribution within a batch.Ideally, the manufacturing processes are tightly controlledto the extent that these distributions average towards a sin-gular value when properly loaded into a case. This wouldassure targeted performance metrics are achieved con-sistently. Individual small-caliber propellant grains are quitesmall and a single cartridge could consist of 10,000 grains.This is beneficial as deviations between grains are generallyintegrated out by the larger bulk properties. Lastly, initialtemperature conditions will contribute to the performanceof a given propellant. While the initial temperature cannotbe controlled in a real-world scenario, a properly equipped

[a] J. J. RitterU.S. Army Research LaboratoryAberdeen Proving Ground, MD 21005 USA*e-mail: [email protected]

[b] C.-F. Petre, P. Beland, C. NicoleDefence Research & Development Center – ValcartierQuébec, QC G3 J 1X5 Canada

Propellants Explos. Pyrotech. 2021, 46, 1–9 1© 2021 Her Majesty the Queen in Right of Canada. Propellants, Explosives, Pyrotechnics © 2021 Wiley-VCH GmbH. Reproduced with the permission of the Ministerof Department of National Defence. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

closed bomb can be controlled in a laboratory to determinehow it affects propellant performance.

Propellant evaluations can be performed in two primarymanners. First, gun firings can be conducted to determinethe muzzle velocity and pressure profile of a cartridge. Thisis useful in many scenarios where more qualitative resultsare acceptable, but this method contains uncontrolled vari-ables, such as bore resistance, that are unrelated to the pro-pellant. The second method to evaluate propellant is aclosed bomb (vessel) [1–3]. A closed bomb is a fixed vol-ume chamber capable of withstanding high pressures, up-wards of 700 MPa in a properly designed vessel. The closedbomb is designed specifically for evaluating propellant as iteliminates variables associated with a gun firing and pro-duces data solely related to the propellant. For this reason,the closed bomb is ideally suited to investigate various pro-pellant or ignition properties of interest as past studieshave demonstrated [4–7]. Knowing some initial propellantproperties, primarily size and thermochemical properties,researchers can evaluate closed bomb data to determinekey propellant characteristics such as burning rate (BR), dy-namic vivacity (L), relative force (RF), and relative quickness(RQ).

A short series of experiments were conducted in thisstudy to evaluate a typical ball powder propellant and de-termine how unexpected and uncontrolled manufacturingor operational changes could affect its performance. For ex-ample, how does a significant change in propellant particlesize distribution affect its performance? As such, an experi-ment was conducted to evaluate the effects of particle sizeon the propellant pressure generation and its burning char-acteristics. In theory, the burning rate of the propellant isconsistent across all grain sizes, but the influence of de-terrent depth and available surface area for a given massmay influence the burning characteristics.

Also, an experiment was furnished to determine thebulk density dependence on grain size. Ball powder is com-prised of a distribution of different grain sizes that rangefrom about 400–710 μm. If grains are segregated into ‘large’and ‘small’ sizes, there may be an influence on the overallpacking density of the propellant.

Lastly, an experiment was conducted to evaluate the ef-fects of temperature on the propellant burning perform-ance. Nitroglycerine (NG), which is the second most abun-dant ingredient in ball powder, has a relatively low boilpoint (50 °C). This translates to a potential migration of NGfrom within the propellant when exposed to high temper-atures for relatively long periods. This could affect the pro-pellant performance, as the local chemistry of the propel-lant grain is changed.

2 Experimental Section

2.1 Closed Bomb

In this study, a RARDE (model CV21, V 700 cm3) closedpressure vessel (Figure 1) was employed to obtain theclosed bomb measurements. It is fitted with an internalsleeve in order to reduce the volume to 188 cm3. This al-lows for safer operations and less propellant being neededper trial. The RARDE closed vessel can be operated to pres-sures up to 250 MPa. A piezoelectric pressure transducerwas used to measure the pressure-time relationship foreach sample. Ignition of the propellant was achieved usingan electric match and a small quantity of black powder, typ-ically 1 g. The burning rate coefficient (β) and pressure ex-ponent (α), as well as the dynamic vivacity, were calculatedfrom the pressure-time data recorded in the closed vessel[8–9] coupled with the impetus and flame temperature datasimulated through the use of the CHEETAH thermochemicalcode [10] using the virial equation of state (BLAKE compati-bility). The XLCB computer code [11–12] was used to per-form the burning rate regressions. The closed vessel tem-perature was maintained at 20 °C by using a jacketcirculating chilled water, except for the tests where a highertemperature was needed. In the hot experiments, hot wateris flowed through the jacket to obtain the appropriatechamber temperature. The primary advantage of the RARDEtemperature compensation is that the entire vessel andcombustion chamber is conditioned to a steady-state targettemperature that can be maintained for an extended peri-od. This eliminates uncertainty of temperature compen-sated propellant being placed into an uncompensatedclosed bomb.

Figure 1. RARDE (model CV21) closed vessel used for propellantburning characterization.

J. J. Ritter, C.-F. Petre, P. Beland, C. Nicole

2 Propellants Explos. Pyrotech. 2021, 46, 1–92© 2021 Her Majesty the Queen in Right of Canada. Propellants, Explosives, Pyrotechnics © 2021 Wiley-VCH GmbH. Reproduced with the permission of the Ministerof Department of National Defence. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

To validate the temperature of the enclosure, three ther-mocouples were installed at various locations and con-nected to a data recorder. Temperature readings were tak-en at the following locations: 1) bath temperature, 2)surface of the enclosure, and 3) air inside the combustionchamber. In this way, proper control of the bath temper-ature can be maintained in order to reach the correct tem-perature inside the enclosure, as well as determine the timenecessary for the combustion chamber to reach equilibriumprior to ignition. Figure 2 illustrates the data to heat thevessel to 70 °C interior temperature.

A second closed vessel was employed for comparisonpurposes. The second closed vessel was a product of Har-wood Engineering. This is nominally a 200 cm3 vessel withhemispherical chamber capable of withstanding 860 MPa[13]. The specific vessel employed had a measured volumeof 209 cm3. The Harwood vessel was employed to achievehigher pressures than the RARDE vessel, specifically gunpressures. No temperature considerations were taken for

the Harwood vessel, and all experiments were conducted ata nominal 20 °C.

2.2 Propellant

Experiments were conducted on two different lots of pro-pellant. The first lot was a bulk powder provided by GeneralDynamics (GD-OTS Canada) in a 2 kg batch. The second lotof propellant investigated was downloaded directly fromtypical 5.56 mm cartridges. Specifically, the propellant is aBall Powder®, a proprietary product from General Dynamics[14]. As the name implies, the powder is nominally sphericalin nature, but actually tends to resemble more of a pancakeshape (figure 3). The size and shape make the powder con-ducive to achieving high loading densities as it packs well.This is particularly important in small caliber ammunitionwhere available cartridge space is at a premium.

Also, a deterrent is added to this propellant during themanufacturing process in order to control the burning pro-file. Ideally, the deterrent penetrates the bulk powder to thesame depth to promote consistent burning behavior; how-ever, a gradient of deterrent to penetration depth is likelypresent. As the name implies, the deterred portion of thepropellant grain will burn slower than the base grain. Whena cartridge with a deterred ball powder is fired, the initialgas generation rate is moderate due to the deterrent. Asthe available volume in the gun chamber is increased fromthe moving projectile, the burning propellant will reach thebase grain and burn faster thus generating gas more quick-ly to fill the expanding volume. Without the deterrent, theinitial pressure would be too great for the gun system anda catastrophic event could occur.

2.2.1 Grain Size

An experiment was conducted to determine the effects ofpropellant grain size on the burning characteristics of theball powder. To experiment, the bulk powder was sievedinto various grain sizes. The sizes were 417–500 μm, 500–600 μm, and 600–710 μm. The propellant that sieved lessthan 417 μm was eliminated from the evaluation, as it onlycomprised 1.7% of the total distribution. A compilation ofthe various sieve sizes associated with the bulk propellant isshown in Table 1. As the table shows, the majority of pow-

Figure 2. Closed bomb temperature conditioning profile.

Figure 3. Ball Powder® under microscope.

Table 1. Propellant size distribution.

Sieve Size (μm) Mass (g) % D50 (μm)

710 6.8 0.3 –600–710 549.1 27.9 699500–600 1188.0 60.4 622417–500 190.0 9.7 544417 33.7 1.7 –



der sieved between 500 and 600 μm, and another quarterbetween 600 and 710 μm. Each size batch was evaluated inthe closed bomb, as well as a sample of the original (bulk)propellant, and calculations were made to determine burn-ing rate, relative force, relative quickness, and dynamic viva-city.

After sieving the propellant into their associated bins,the particle size distribution was determined via a MalvernMastersizer 2000. The Mastersizer 2000 is capable of meas-uring particle sizes as small as 0.020 μm. For data reductionpurposes, the particle size chosen for each sieve size wasthe D50 value determined by the Malvern, which are shownas part of Table 1. The bulk powder D50 was measured at634 μm. As the table illustrates D50 values are larger thanthe associated sieve size. This phenomenon can be attrib-uted to the non-uniform nature of the propellant as de-picted in figure 3, and the assumption that the propellant isa sphere.

2.2.2 Temperature Effects

In addition to the potential migration of NG from within thepropellant when exposed to high temperatures for rela-tively long periods, ball powder propellant burning rate isalso known to be temperature-dependent [2]. An increasein initial temperature will result in an increased burning rateof the propellant. To investigate the effects of temperatureon propellant burn rate a series of closed bomb experi-ments were performed at elevated temperatures on thebulk powder. Standard, ambient temperature for such ex-periments is 20 °C. These experiments were conducted toprovide a baseline performance at ambient temperature.For the hot temperature shots, experiments were per-formed at 60 °C, 70 °C, and 80 °C. Evaluations in the closedbomb were performed on both the bulk lot and cartridgedownloaded propellant. Data analyses were performed toevaluate the burning rate of the propellants, relative force,relative quickness, and dynamic vivacity.

2.2.3 Volumetric Effects

Lastly, volumetric analysis was conducted on the propellantto determine its bulk density at various grain size batches(i. e. 417–500 μm, 500–600 μm, and 600–710 μm). In this ex-periment, the powder was poured into a 10 mL graduatedcylinder and then vibrated for one minute to promote com-paction. The bulk density was then derived from the massof the powder and the volume it occupied.

Due to constraints on propellant availability, specificallyfrom the downloaded cartridges, not all experiments wereconducted on both lots of propellant. A matrix of experi-ments conducted is shown in Table 2 with the associateddata collected for analyses.

3 Results and Discussion

3.1 Propellant Grain Size Effects

Closed bomb experiments were conducted on the sievedpropellant to determine effects of grain size on the burningrate (BR). The propellant was from a bulk propellant lot pro-vided by GD-OTS Canada. The RARDE closed bomb wasloaded with 32 g of propellant per shot, or 0.17 g/cc load-ing density. Between 2–4 shots were performed on eachsieve size to generate data for analyses. Two experimentswere conducted on the 417–500 μm grain size, three ex-periments were conducted on the 500–600 μm grain sizeand four experiments were conducted on the 600–710 μmgrain size to generate the following data.

Burning rate is expressed by Vieille’s Law in the form of,

BR P (1)

where BR is the burning rate, β is the burning rate co-efficient, P is the pressure, and α is the pressure exponent.

Figure 4 shows the burning rate data on a log-log plot,including the derived equations. The reference propellant isthe bulk, as received propellant. As the plot indicates, theburning rate for the bulk powder is the same as the smallersieved sizes of 417–500 μm and 500–600 μm propellant.The larger grain sizes exhibited a higher burning rate at agiven pressure.

Table 2. Matrix of Experiments.

Experiment Bulk Downloaded Data

Temperature X X BR, RQ, RF, LGrain Size X BR, RQ, RF, LVolumetricDensity

X Bulk Density

Figure 4. Propellant burning rate as a function of grain size.



It would be expected that the bulk BR was similar to theBR of the grain size that primarily composes the bulk pow-der, namely the 500–600 μm grains, which comprises 61%of the bulk powder. There are a few possible explanationsto the higher burning rate associated with the larger grainsize, both relate to the role of the deterrent. Assuming anequal depth distribution of deterrent per grain, the resultwould be that larger grains contain a higher ratio of basegrain material to deterrent profile. This would result inhigher availability of energy for a given mass of propellant.Conversely, the diffusion of the deterrent may not pene-trate as deep into the larger volume associated with thelarger grains, creating a shallower deterrent layer. This sce-nario would also result in a higher base grain to deterrentratio compared to the smaller grains. As a result, at100 MPa, the bulk propellant burns at 8.47 cm/s, whereasthe segregated larger grain burns at 11.15 cm/s, which rep-resents a 32% increase.

Relative quickness (RQ) is a propellant property gen-erated from the closed bomb data. The term relative quick-ness is a measure of how quickly a propellant burns con-cerning a reference propellant. In this case, the referencepropellant is the bulk powder and the comparison is beingmade against the various grain sizes being investigated. Tocalculate the RQ, the rate of change in pressure, dP/dt, istaken at four different pressure values 27%, 40%, 53%, and66% with respect to the PMax value. Each value is comparedto the respective reference value. The four resultant valuesare then averaged to determine an overall RQ for propel-lant or in this instance grain size. Table 3 shows the sum-mary data of calculated RQ values. The RQ values are most-ly around the nominal bulk propellant quickness with a fewexceptions for the larger grains.

Table 4 shows the relative force of each trial associatedwith the differing grain size. To calculate relative force themaximum pressure for each subject propellant is comparedagainst the PMax of the reference propellant, in this case, thebulk propellant. As shown, there was little dependence ofgrain size as it relates to the relative force of the propellant.Coupled with the BR and RQ information this suggests thatthe larger grain sizes did not necessarily produce more

peak pressure than the other grain sizes, but they did ob-tain peak pressure sooner.

3.2 Propellant Temperature Effects

Closed bomb experiments were conducted to determinethe influence of temperature on the propellant. Experi-ments were conducted on both the bulk lot provided byGD-OTS Canada, as well as the lot downloaded from 5.56-mm ammunition. Experiments consisted of shots evaluatedat a reference, ambient temperature (20 °C), and hot tem-peratures of 60 °C, 70 °C, and 80 °C. From the closed bombevaluations data was analyzed to determine burning rate,relative force, relative quickness, and dynamic vivacity.

The burning rate of the propellant did exhibit some de-pendence on the initial temperature. Both figures 5 and 6show the burning rate as a function of temperature for thedownloaded and bulk propellant lots, respectively. Thecharts show a general trend of increased burning rate as in-itial temperatures are increased. There also appears to be agreater divergence at pressures above 70 MPa. For thedownloaded propellant, at 100 MPa the burning rate of theambient (20 °C) propellant was 7.81 cm/s, while the hot(80 °C) scenario produced a burning rate of 10.13 cm/s. Thebulk powder showed similar temperature dependence at100 MPa where the ambient burning rate was 9.54 cm/sand 11.87 cm/s at hot. Figure 7 illustrates a comparison ofthe two lots of propellant at ambient and hot (80 °C) tem-peratures. The figure also shows how lot-to-lot variability

Table 3. Relative Quickness as a function of propellant grain size.

Grain Size(μm)

417–500 500–600 600–710

RelativeQuickness

100 97 106 100 100 118 101106 102

Table 4. Relative Force for bulk propellant.

Grain Size (μm) Reference 417–500 500–600 600–710

PMax (MPa) [164] 164 164 165 164 167 170 165 167 166Relative Force 100 100 101 100 102 104 101 102 101

Figure 5. Burning rate of cartridge downloaded propellant as afunction of temperature.



can exist within differing lots of propellant. This variability isacceptable as long as the propellant is within product spec-ification. Consistent ammunition performance can still beachieved with these differences by altering the charge ofthe cartridge. During the manufacturing process, the manu-facturer would load a little less of the “faster” burning pow-der into a cartridge to get similar performance levels to the“slower” burning powder thus providing for consistent car-tridge performance between various propellant lots.

Table 5 illustrates the relative quickness and relativeforce of each propellant at the evaluated temperatures.There is some discrepancy in the RQ values at 60 °C, how-ever, both lots of propellants exhibited near-identical RQvalues at the higher 70 °C and 80 °C temperatures with bothexhibiting quicker gas generation. The changes in RF aremore subtle than RQ. For the cartridge downloaded propel-lant there was no change at 60 °C and a 4% increase in RFat 70 °C and 80 °C. The bulk powder showed a slight RF in-crease at all elevated temperatures of 2–3%.

Lastly, vivacity plots (figures 8 and 9) were generatedfrom the closed bomb data. This information is primarilyused to ensure the propellant is burning as intendedwhether it is progressive, regressive, or neutral. Ball powderby nature should burn in a regressive nature, as there is lesssurface area available to burn as the propellant continuesto deflagrate from the outside inward. Deterred ball pow-der does create a more complex situation where the avail-able energy is not homogeneous throughout the grain.Both plots clearly show a regressive deflagration profile

Figure 6. Burning rate of bulk propellant as a function of temper-ature.

Figure 7. Burning rate comparison of downloaded and bulk propel-lant lots as a function of temperature.

Table 5. Summary Relative Quickness and Relative Force.

Temperature Relative Quickness Relative Force(°C) Download Bulk Download Bulk

20 (Ref) – – – –60 102 117 100 10270 124 122 104 10380 122 122 104 102

Figure 8. Vivacity for cartridge downloaded powder.

Figure 9. Vivacity for bulk powder.



once the pressure reaches 40–50% of peak pressure. Over-all, the plots did not exhibit any abnormalities.

3.3 Closed Vessel Comparison

In order to evaluate the propellant at higher pressures,namely gun pressures, experiments were conducted in theHarwood closed vessel to replicate those performed in theRARDE vessel. Experiments were only conducted on thesieved, bulk propellant received from GD-OTS Canada.There was not enough propellant for the lowest 417–500 μm size, but the other two sizes were performed alongwith the bulk as received powder, noted as the reference.

In the Harwood, loading densities of 0.17, 0.25, and 0.30were conducted to achieve desired pressure values, withthe maximum pressure of 380 MPa being obtained at thehighest loading density. This represents typical 5.56-mmgun operating pressures. Figure 10 shows a summary ofthose results, and similar to the results from the RARDE ex-periments (Figure 4), the burning rate of the larger sievedparticles (600–710 μm) exhibit a higher burning rate at thehigher pressures. At 100 MPa the bulk propellant had a cal-

culated burning rate of 8.92 cm/s, and the 600–710 μm par-ticles had a burning rate of 11.05 cm/s. These values arestatistically the same as the RARDE results of 8.47 and11.15 cm/s, respectively.

3.4 Volumetric Analysis

Volumetric analysis was conducted to define the propellantbulk density as a function of grain size. In this manner, itcould be determined if there is any influence on how thegrains pack together when they were sieved to varioussizes. The results from the analysis can be seen in table 6,where there is no meaningful relationship between thegrain size and corresponding bulk density. Measured differ-ences were less than 1% between the extreme largest andsmallest grains. This seems reasonable as ball powder hasvery good flow characteristics resulting in minimal voidspaces.

4 Conclusion

Closed bomb experiments were performed to evaluate theeffects of temperature and grain size on the burning rate ofa deterred ball powder, specifically powder loaded into5.56 mm cartridges. The closed bomb is a constant volume,laboratory evaluation tool that eliminates uncertainty asso-ciated with weapon system firings. In this respect, only thepropellant is being examined and influences related to pri-mer performance, expanding volumes, and bore resistanceare eliminated. One deviation in the closed bomb experi-ments was the departure from nominal gun pressures. Typi-cal 5.56 mm gun pressures are 380 MPa, whereas the ma-jority of the experiments were conducted in the 130 MPapressure regime. To mitigate this shortcoming, experimentswere also conducted in a Harwood closed vessel up to380 MPa and the results of these experiments tracked wellwith the lower pressure results from the RADRE closed ves-sel.

The experiments evaluated two lots of propellant. Bulkball powder provided by GD-OTS Canada, and propellantdownloaded from inventory ammunition. For particle sizeexperiments, the powder was manually sieved and sepa-rated. Particle sizes were binned and evaluated between417–500 μm, 500–600 μm, and 600–710 μm. For the tem-perature evaluations, the propellant was evaluated at am-bient temperature (20 °C) as well as elevated temperaturesof 60 °C, 70 °C, and 80 °C. Closed bomb data were analyzedto determine propellant burning rate, relative force, relativequickness, and dynamic vivacity values.

Results from the experiments indicate that both lots ofpropellant functioned in an as intended fashion. Datashowed some minor differences between the lots, partic-ularly with respect to their burning rate but values werewithin nominal tolerances. Particle size appeared to influ-

Figure 10. Burning Rate as a function of grain size for bulk powderin a Harwood closed bomb.

Table 6. Bulk Density of Ball Powder Relative to Grain Size.

Granulation Vol. Mass Bulk Density Bulk Density Ave

(μm) (cc) (g) (g/cc) (g/cc)

710–810 4.3 4.66 1.084 1.084

600–710 7.5 8.04 1.0727.0 7.66 1.094 1.0869.4 10.25 1.090

417–500 6.5 7.12 1.0956.0 6.53 1.088 1.0937.0 7.67 1.096



ence the burning rate, where the larger particles had a ten-dency to burn faster. This is likely the result of the deterringprocess and a higher base grain to deterrent ratio whencompared to the smaller particle sizes.

As anticipated, the temperature also exhibited an influ-ence on the burning rate of the powder. Moderate changesin initial temperature did not show appreciable changes,but at the higher temperatures, the burning rate of the pro-pellant was noticeably increased. There also appeared to bea greater divergence in burning rate as the pressure in-creased.

Lastly, a volumetric density study was conducted to de-termine the bulk packing density as a function of grain size.The results did not demonstrate a density dependence onthe particle size. Ball powder is specifically manufactured tohave good flow properties and fills voids in a given spacequite well so this finding is reasonable, if not expected.

These results suggest that there are inherent perform-ance differences of the individual grains that comprise aball powder lot, and there are definitely lot-to-lot variations.However, ball powder is relatively small with thousands ofgrains of propellant consisting of a single charge. This al-lows the grain-to-grain variations to be integrated out intoa single burning rate value for a given lot of propellant thusproviding consistent cartridge performance. Performancevariations between lots can still exist, but these can becompensated for by small variations in the cartridge load-ing density.

Data Availability Statement

The data that support the findings of this study are avail-able from the corresponding author upon reasonable re-quest.

References

[1] E. Degirmenci, Effects of Grain Size and Temperature of Dou-ble Base Solid Propellants on Internal Ballistics Performance,Fuel. 2015. 146, 95–102.

[2] C. F. Petre, J S. Binette, FSAR WBE 1.4.3: Internal Ballistics Evalu-ation of Lightweight 7.62 x 51 mm Polymer and Stainless SteelCased Ammunition (U), DRDC-RDDC-2021-R004, Defence Re-

search and Development Center–Valcartier, Quebec QC, Cana-da 2021.

[3] K. M. Boulkadid, D. Trache, S. Krai, M. H. Lefebvre, L. Jeunieau,A. Dejeaifve, Estimation of the Ballistic Parameters of DoubleBase Gun Propellants, Propellants Explos. Pyrotech. 2020, 45,751–758.

[4] L. Jeunieau, M. H. Lefebvre, A. Papy, M. C. Pirlot, P. Guillaume,Influence of the Size Distribution on the Combustion Rate ofSpherical Propellant, 20th International Symposium on Ballistics,Sept 23–27, 2002, Orlando, FL, USA.

[5] L. Jeunieau, M. H. Lefebvre, P. Guillaume, Closed Vessel TestSimulations of Deterred Propellant: Influence of the IgnitionHomogeneity. 38th International Annual Conference of ICT,2007.

[6] L. Jeunieau, M. H. Lefebvre, A. Papy, M. C. Pirlot, P. Guillaume,C. Reynaud, Spherical Deterred Propellant: Influence of theConcentration Gradient on the Burning Rate Calculation. Inter-national Annual Conference; 34th, Institut Chemische Tech-nologie; Energetic Materials: Reactions of Propellants Explosivesand Pyrotechnics, 2003.

[7] R. Trebinski, Z. Leciejewski, Z. Surma, B Fikus, Some Consid-eration on the Methods of Analysis of Closed Vessel Test Data.29th International Symposium on Ballistics, May 9–13, 2016, Ed-inburgh, UK.

[8] K. W. Klingaman, J. K. Domen, The Role of Vivacity in ClosedVessel Analysis, JANNAF Propellant Development and Character-ization Subcommittee Meeting, April 18–19, 1994, NASA Ken-nedy Space Center, FL, USA.

[9] W. Oberle, Dynamic Vivacity and Its Application to Conventionaland Electrothermal-Chemical (ETC) Closed Chamber Results, ARL-TR-2631, US Army Research Laboratory, Aberdeen ProvingGround, MD, USA 2001.

[10] S. Bastea, L. E. Fried, K. R. Glaesemann, W. M. Howard, I. W.Kuo, P. C. Souers, P. A. Vitello, Cheetah 7.0 User’s Manual, LLNL-SM-599073, Lawrence Livermore National Laboratory, Liver-more, CA, USA 2012.

[11] B. E. Homan, A. A. Juhasz, XLCB: A New Closed-Bomb Data Ac-quisition and Reduction Program, ARL-TR-2491, US Army Re-search Laboratory, Aberdeen Proving Ground, MD, USA 2001.

[12] A. Celmins, Solid Propellant Burning Rate Measurements in aClosed Bomb, BRL-1840, US Army Ballistic Research Laboratory,Aberdeen Proving Ground, MD, USA 1975.

[13] Retrieved from https://www.harwoodeng.com/products/spe-cial-purpose-vessels/powder-bomb-vessel/ September 2020.

[14] Retrieved from https://www.gd-ots.com/propellant-and-pro-pulsion/st-marks-powder-propellants/ July 2020.

Manuscript received: October 27, 2020Revised manuscript received: December 4, 2020

Version of record online: February 3, 2021



FULL PAPER

J. J. Ritter*, C.-F. Petre, P. Beland, C.Nicole

1 – 9

Influence of Particle Size and Tem-perature on the Burning Rate ofSmall Caliber Ball Powder

DOCUMENT CONTROL DATA *Security markings for the title, authors, abstract and keywords must be entered when the document is sensitive

1. ORIGINATOR (Name and address of the organization preparing the document. A DRDC Centre sponsoring a contractor's report, or tasking agency, is entered in Section 8.)

Wiley

2a. SECURITY MARKING (Overall security marking of the document including special supplemental markings if applicable.)

CAN UNCLASSIFIED

2b. CONTROLLED GOODS

NON-CONTROLLED GOODS DMC A

3. TITLE (The document title and sub-title as indicated on the title page.)


4. AUTHORS (Last name, followed by initials – ranks, titles, etc., not to be used)

Ritter, J.; Petre, C.-F.; Béland, P.; Nicole, C.

5. DATE OF PUBLICATION (Month and year of publication of document.)

February 2021

6a. NO. OF PAGES (Total pages, including Annexes, excluding DCD, covering and verso pages.)

9

6b. NO. OF REFS (Total references cited.)

14

7. DOCUMENT CATEGORY (e.g., Scientific Report, Contract Report, Scientific Letter.)

External Literature (P)

8. SPONSORING CENTRE (The name and address of the department project office or laboratory sponsoring the research and development.)

DRDC – Valcartier Research Centre Defence Research and Development Canada 2459 route de la Bravoure Québec (Québec) G3J 1X5 Canada

9a. PROJECT OR GRANT NO. (If appropriate, the applicable research and development project or grant number under which the document was written. Please specify whether project or grant.)

02aa - Future Small Arms Research (FSAR)

9b. CONTRACT NO. (If appropriate, the applicable number under which the document was written.)

10a. DRDC PUBLICATION NUMBER (The official document number by which the document is identified by the originating activity. This number must be unique to this document.)

DRDC-RDDC-2021-P061

10b. OTHER DOCUMENT NO(s). (Any other numbers which may be assigned this document either by the originator or by the sponsor.)

DOI: 10.1002

11a. FUTURE DISTRIBUTION WITHIN CANADA (Approval for further dissemination of the document. Security classification must also be considered.)

Public release

11b. FUTURE DISTRIBUTION OUTSIDE CANADA (Approval for further dissemination of the document. Security classification must also be considered.)

12. KEYWORDS, DESCRIPTORS or IDENTIFIERS (Use semi-colon as a delimiter.)

Burning rate; propellant; closed vessel; 5.56 mm; dynamic vivacity

13. ABSTRACT/RÉSUMÉ (When available in the document, the French version of the abstract must be included here.)

The performance of a small caliber propellant is influenced by many factors. Foremost is the chemical composition, however, other factors such as the physical properties of the propellant, the weapon system, and the operating conditions can also greatly influence the performance of a propellant. In this study, researchers investigated the influence of particle size and temperature on the performance of small caliber, ball powder propellant. Particle size is important as it provides the initial surface area available for a propellant to begin the deflagration process. The geometry of the grain will dictate the manner in which the deflagration progresses: progressively, regressively, or neutral. The initial temperature of the propellant also has a direct influence on propellant performance. Evaluations were conducted in a constant volume, temperature controlled closed vessel to obtain pressure-time data for the various experiments. The data coupled with the propellant thermochemical properties were used to calculate the burning rate coefficient (β) and pressure exponent (α) of the propellant. Dynamic vivacity, relative force, and relative quickness values are also reported.

influence of particle size and temperature on the burning

Documents