PROBLEMY MECHATRONIKI UZBROJENIE, LOTNICTWO , INŻYNIERIA
BEZPIECZEŃSTWA
ISSN 2081-5891 11, 2 (40), 2020, 9-24
PROBLEMS OF MECHATRONICS ARMAMENT, AVIATION, SAFETY ENGINEERING
New Cartridge Design for Assault Rifle
Peter LISÝ*, Martin DANIEL
Department of Mechanical Engineering Armed Forces Academy of Gen. M.R. Štefánik, Demänová 393, 031 01 Liptovský Mikuláš 6, Slovak Republic *Corresponding author’s e-mail address and ORCID: [email protected]; https://orcid.org/0000-0001-8721-2660
Received by the editorial staff on 18 May 2018 The reviewed and verified version was received on 02 June 2020
DOI 10.5604/01.3001.0014.1989
Abstract. The article deals with the possible design of a new cartridge for an automatic assault rifle. This hypothetical design is based on the analysis of five automatic assault rifle cartridges which are currently used in armies: 7.62×51 mm NATO, 7.62×39 mm M 43, 5.56×45 mm NATO and also another two cartridges which are under testing both 6.8×43 mm Rem. SPC and 6.5×38 mm Grendel. The analysis of a new cartridge including internal ballistics, external ballistics, and terminal ballistics energy disposed to the target upon an impact is introduced in the article. The goal was to create a cartridge that would have better ballistic performance than 5.56×45 mm NATO and it would still possess enough accuracy of fire and speed, so that it could dispose at least minimal kinetic energy necessary to incapacitate individuals. Also it is important to maintain the constancy of this effect for the long distance shooting, somewhere around 500 m, during battles in an open area (effective range of 5.56×45 mm automatic assault rifles is normally of about 300 m what only suffices in close quarter battles).
This work has been compiled from the paper presented during the 12th International Armament Conference on Scientific Aspects of Armament & Safety Technology, Jachranka, Poland, September 17-20, 2018
10 P. Lisý, M. Daniel
To achieve it, the bullet must have the higher sectional density than the 5.56×45 mm cartridge. The sectional density reflects the capability of bullet to penetrate through the human tissue within the requirements of wound ballistics. Based on the analysis, the value of sectional density should be approximately of 0.21 g/mm2. The function of fully automatic firing depends on the size of the recoil energy of a weapon which is also related to the muzzle energy that cannot surpass the amount of 2 500 J. The new cartridge design is based on the 6 mm Scenar bullet (FMJ - Full Metal Jacket bullet with a weight of 5.8 g) made by the Lapua Company. All the ballistic parameters must be within the intervals of strength and construction possibilities of small arms ammunition. To create a possible variation of the mentioned cartridge where its bullet will be powered by a nitrocellulose propellant (originally made in Czech Republic), a new cartridge case will be created. Keywords: ammunition for automatic assault rifles, ballistics
1. INTRODUCTION
A mixture of the close-quarter combat and long-range contacts again raised questions of the stopping power of NATO ammunition. The standard NATO ammunition with a green tip is failing to stop attackers. Also, it cannot fight with calibre 5.56×45 mm NATO (range up to 600 m) against 7.62×54 R mm Russian calibre which is using a light machine gun up to 900 m [1]. Majority of fighting contacts occurs at either very close range or at the ranges between 500 m to 900 m (Table 1). Table 1. Fighting contacts [2]
It is clear from Table 1 that these ranges are possible to cover only with established weapon 7.62×51 mm general purpose machine gun. The calibre 5.56×45 mm has a lack of the reaching the enemy at those ranges because this calibre is sufficient only at the proper range, but for the longer ranges 7.62×51 mm calibre is necessary. Here is a needful research for the higher performance rounds with a higher efficiency at the longer ranges. The waiting is, that next generation of assault rifle to replace the 5.56 mm SA80 around 2020 [3]. New Cartridge Design for Assault Rifle 11
The 5.56×45 mm NATO cartridge for assault rifle and a light machine gun is under criticism due to extensive combat experience. This calibre was always controversial choice due to a small size and a lack of power [4]. The complaints are from British soldiers, too. It is mainly for: - poor long-range effectiveness; - erratic efficiency even at short-range; - a lack of suppressive effect; - poor barrier penetration. Accordingly, from German troops are complains on: - lack of stopping ability; - penetration. The experiences both from Iraq where is the urban fight and Afghanistan where are the long-range engagements mentioned that achieving the best compromise will involve several variables [5]: - hit probability (a function of trajectory, flight time and wind drift); - required maximum range; - terminal effectiveness (against soft and hard targets) at different ranges; - acceptable cartridge weight and recoil. The answer for the raising of requirements on the base of complex operational environment for the international armed forces activity is in the ultimate consequence graduation requirements on the alternative design weapon and ammunition with the trend on improvement the mobility (manoeuvrability), precision and stopping effect. At the present time, it is going the research in design of small arms including implementation of shorter barrels and carbines for the close quarter battle and personal defence weapon. Accordingly, it is going the research for alternative calibres from the reason of optimization of their weight and stopping effect, spread of applicability of suppressors for reduction of unmask symptoms and area of integrated fire system for improvement in precision on the lowest tactical level. The operational requirements were determined on the conference “Future Soldier Technology” in London on the 3rd of March 2018 [6]. North Atlantic Treaty Organization, as an alliance, is trying to implement its common ammunition into the armies which are being the part of the organization. Nowadays, NATO possesses two main cartridges for assault rifles which are being normally used in asymmetrical wars in the Middle East – 5.56×45 mm and 7.62×51 mm. The close quarter battles offer better opportunity for using the 5.56×45 mm cartridge because it has enough ballistic performance for firing at short distances but it lacks the capability of incapacitating an individual at longer distances (more than 300 m). However, also its behaviour on a short distance is like an arrow, i.e., a small bullet with high speed overruns a body and makes a small permanent cavity which means that the bullet does not transfer enough kinetic energy to the body and does not stop to fight the individual. 12 P. Lisý, M. Daniel
On the other hand, the 7.62×51 mm cartridge over the fact of much better ballistic performance appears to be a twice heavier than the smaller cartridge of 5.56×45 mm (Table 2). Also, from Table 2 we can compare other cartridges’ parameters for assault rifles and Fig. 1 shows the designs comparison of the mentioned cartridges.
Table 2. Parameters of assault rifles cartridges [7]
7.62×39 mm 7.62×51 mm 5.56×45 mm 6.8×43 mm 6.5×38 mm Cartridge M43 NATO NATO SS109 Rem. SPC Grendel FMJ FMJ FMJ FMJ bullet weight 7.9 9.33 4 5.8 7.45 mq [g] muzzle velocity 730 800 906 823 785 vm [m/s] muzzle energy 2 105 2 986 1 642 1 964 2 295 Em [J] sectional density 0.173 0.205 0.165 0.175 0.205 SD [g/mm2] barrel length 415 450 450 368 410 lbar [mm] effective range 800 600 600 600 300 L [m] cartridge 16.3 25.4 11.8 14.7 16.8 weight – mc [g]
Fig. 1. Cartridges (left) 7.62×39 mm M43; 7.62×51 mm NATO; 5.56×45 mm NATO; 6.8×43 mm Rem. SPC; 6.5×38 mm Grendel [7]
New Cartridge Design for Assault Rifle 13
The performance of the different calibres can be compared by their kinetic energy value. In Fig. 2, we can see the courses of the bullet energy Eq vs the distance L for the four cartridges listed in Table 1, where it is evident that the more aerodynamic bullet of the 6.5×38 mm Grendel, but with the weight of 8 g, keeps the kinetic energy for the long distance the best. At the distance of 600 m it has approximately the same energy as the 7.62×51 mm bullet, 1.5 times higher energy like the 6.8×43 mm Rem. SPC and 3.3 times like the 5.56×45 mm. But, the 8 g 6.5×38 mm Grendel bullet has the muzzle energy of 2528 J and the sectional density of 0.24 g/mm2 which are both too high for keeping a sustainable fire due to the high recoil energy Er = 5.06 J for 4 kg heavy weapon.
Fig. 2. Bullet energy value for different calibres [8, 9] For alliance like the NATO, it would be better to provide material supply just for one type of a cartridge, which would possess the ballistic performance somewhere between these two types of the rounds – it means better the ballistic performance (accuracy of fire, muzzle velocity, energy disposed to target upon impact) also for longer distances (target distant of about 500 m, up to 600 m). And the individual could be still a capable to carry at least the same number of rounds in the magazine for 5.56 mm automatic assault rifle. Here, there exist some intentions which offer an alternative for the common ammo like 6.5×39 mm Grendel or 6.8×43 mm Rem. SPC, but we tried to create a possible cartridge with 6 mm calibre.
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2. CARTRIDGE DESIGN
At creating a new cartridge design for the middle ballistics performance it is important to achieve a proper rate between the performance at long range and recoil of automatic assault rifle (AAR), i.e., for shooting with controlled full-auto fire. From Table 2, we can see that for the lesser recoil AAR, the calibre could be less than 7 mm and from another side for the better stopping effect, the calibre could be bigger than 6 mm include. When the bullet sectional density is bigger, the bullet will has more performance at the longer distance but the muzzle energy could not exceed the value of 2 500 J for the recoil reason. At present, it is the requirement to use the same cartridges for AAR-s and light machine guns. One of the main parts of a cartridge is a bullet which is a cylindrically shaped lead or alloy that engages with the rifling of the barrel. The bullet consists of a steel penetrator and a copper alloy jacked (the copper alloy reduces barrel wearing and helps to prevent the bullet from striping or jumping the rifling during firing). To obtain high velocities, which we need for the military applications, the full metal jacketed bullet was chosen. The bullets are mainly characterised by the ballistic coefficient which determines how well the bullet can maintain a velocity. The bullets with the less ballistic coefficient maintain the velocity better. The ballistic coefficient BC can be calculated:
𝑖∙푑2 퐵퐶 = ∙ 103 [m2/kg] (1) 푚푞 where i is the bullet´s form factor; d – is the calibre; mq – is the bullet weight. Very important characteristic of the bullet, which is applied not only in external ballistics but also in internal and terminal ballistics, is the sectional density - SD. The sectional density also defines range, graphic of bullet path, and duration of bullet flight. With increasing the sectional density upon firing with the same angle, the range is longer, and the path of flight is flatter. The sectional density can be calculated: 4∙푚 푆퐷 = 푞 [g/mm2] (2) 휋∙푑2 Both the BC and SD have influence on the range and effect on the target. To reach the enough ballistic performance, also for the longer distances, there was chosen the Lapua Scenar bullet with the calibre of 6 mm and weight of 5.8 g (Fig. 3), which is used at present by the world´s top competitors and it gives the superb results at the long ranges shooting [10].
New Cartridge Design for Assault Rifle 15
Fig. 3. Lapua Sierra 6 mm calibre Scenar [11]
This bullet has the ballistic coefficient for long range (G7) equal to 9.61 m2/kg, while the 5.56×45 mm NATO has the ballistic coefficient (G7) of 13.42 m2/kg. Figure 4 shows the difference of the drag bullet coefficient in dependence of the Mach number for 6 mm Scenar bullet for the both, ballistic coefficient G1, which is used usually, and G7 which is used for a long range.
Fig. 4. Drag bullet cx vs Mach number for 6 mm Scenar bullet [11]
From Figs. 5-6 we can see dependence, the 6 mm Scenar bullet energy Eq, the speed vq, the deviation wd and the path qp versus the distance L. Figure 5 shows the bullet parameters dependences at 4 m/s side-wind. Figure 6 shows the bullet paths at the scope of 40 mm above the centre line of a barrel at three different rifle aiming on 100 m, 300 m, and 600 m, where we can see the impact points above or below the line of sight.
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Fig.5. Dependency bullet parameters vs distance at 4 m/s side-wind [10]
Fig.6. Bullet path vs distance at scope 40 mm above centre line of barrel [10]
The Lapua firm is best known for its experiences and better possibilities of the manufacture and the offer of a new ScenarL bullet (Fig. 7). The differences between both the Scenar and ScenarL bullets are these that new ones have a new line, better concentricity of a jacket wall, a less weight variation, and a dimensional uniformity and other parameters are the same. These new things offer the better possibility of a fire precision. New Cartridge Design for Assault Rifle 17
Fig. 7. Comparison Scenar and ScenarL bullets [10]
The chosen ScenarL bullet, for a possible military cartridge, is capable of maintaining the velocity in a better way than the bullets mentioned in Table 2 and it would strongly affect the target and more deeply penetrate into the armour or human tissue. This bullet at the range of 548 m has the velocity of 529 m/s and at zero speed of wind has the deviation of 72 mm (Fig. 8). Because the cartridge case has no good proportions, mainly its diameter, therefore we design a new cartridge case.
Fig. 8. Deviation of 6 mm ScenarL bullet [12]
In Figure 9, it is a design for the new cartridge case which was created for 6 mm bullet ScenarL with its muzzle velocity of 802 m/s at 372 mm barrel length. The overall length of the calculated cartridge case is 44.06 mm. In Fig. 10 there are compared two cartridges, i.e., the original cartridge design for 6×40 mm ScenarL, made by LAPUA company and the new cartridge case for the same bullet designed by us.
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Fig. 9. Cartridge case for the new cartridge
Fig. 10. Comparison two cartridges 6×44 mm new and 6×40 mm Lapua ScenarL [13]
It is evident from this comparison that the new cartridge is slimmer, and its maximum diameter of the cartridge case is 10.9 mm and the original maximum cartridge case diameter is 11.96 mm. The overall length of the cartridge is 61.875 mm for the new one and 61.2 mm for the original one. The calculation of internal ballistics for the new cartridge was made by thermodynamic interior ballistic model. The classical internal ballistics equations can be written as follows:
d푧 푢1 = 푓(푝) d푡 푒1 휓 = 휅푧(1 + 휆푧 + 휇푧2)
푒1 푒1 (3) 휓 = (1 + ) 푧 − 푧2 푙 푙 2 1 푚휔 푥 푝푥 = 푝푞 {1 + 푘휒 [1 − ( ) ]} 2 휑1푚푞 푙푐ℎ푙푞 New Cartridge Design for Assault Rifle 19 where: z is the propellant relative burnt thickness; u1 is the unit speed of burning; e1 is the half thickness of propellant; f(p) is the pressure function; κ, λ, and μ are the internal ballistic parameters related to propellant shape; l is the length of propellant grain; px is the immediate pressure inside a barrel; pq is the pressure at the base of projectile; kx is the coefficient of loses; mω, mq are the propellant and projectile weights, respectively; φ1 is the power coefficient; x is the immediate distance from base of chamber; lch is the chamber length; lq is the immediate path projectile.
The bullet was taken 6 mm Lapua ScenarL with the weight of 5.8 g, how it was mentioned earlier, and a powder gun was taken the nitrocellulose propellant S-053 which is made in Czech Republic. This propellant has been used for a long-time for 7.62 mm assault rifle, both in Slovak and Czech Republic. The parameters of S-053 propellant are the force f = 1.0132·106 J/kg and the co- volume α = 0.9242 m3/kg, and is reliable. The propellant is made in the form of short tubes with a deterrent which burn at the first half period as progressive and the second half as degressive. The maximum computed pressure was 327 MPa and the muzzle velocity was 802 m/s. We could suppose that this pressure will make a lower recoil force and less disturb the barrel to vibration than the pressure of the 7.62×51 mm NATO (420 MPa) cartridges. From Table 3, we can compare 6 mm ScenarL parameters with further cartridges. The parameters from Table 3 show that the 6×44 mm new cartridge with the ScenarL bullet has the highest ballistics coefficient, which supposes the better bullet stability during a flight. The bullet has the good sectional density what means, that it will be the better transfer of a kinetic energy to the human body, i.e., it will have the better stopping power. Moreover, only the 372 mm long barrel for an assault rifle will give the good possibility for a manoeuvrability and the bullet velocity of 802 m/s also will give the possibility of the shoot up to 600 m with a good precision, as is evident from Fig. 8. The shorter barrel is stiffer than the longer one and a vibration is smaller during the shoot, therefore the shorter barrel is more precise [14, 15, 16]. The bullet muzzle energy of 6×44 mm is higher than of 5.56×45 mm, but enough smaller than of 7.62×51 mm NATO.
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We can compare also from Table 3 the recoil energy Er when we will suppose the weight of 4 kg of an assault rifle for each mentioned calibre. From this, it is evident that the new cartridge will have very low recoil energy what is good for an automatic fire.
Table 3. Basic parameters of selected cartridges [7, 17, 18] m BC G-7 SD Vm Em Er lbar lcar Cartridge q [g] [kg/m2] [g/mm2] [m/s] [J] [J] [mm] [mm] 7.62×39 mm 7.9 13.29 0.173 730 2 105 4.16 415 56.00 M43 7.62×51 mm 9.33 9.95 0.205 800 2 986 6.96 450 69.90 NATO 5.56×45 mm 4.0 13.42 0.165 906 1 642 1.64 450 57.40 NATO 6.5×38 mm 5.8 11.02 0.175 823 1 964 2.85 368 57.50 Grendel 6.8×43 mm 7.45 12.48 0.205 793 2 342 4.26 457 57.40 Rem. SPC 6×44 mm 5.8 9.61 0.205 802 1 865 2.71 374 61.875 new
The loss of the bullet velocity and energy towards the target is influenced mainly by the ballistic coefficient and amount of the sectional density. For the new cartridge, the analysis of outer ballistics of the ScenarL bullet by the PM_Ballistics program was performed. From Fig. 11 we can see the courses of three parameters – vq, Eq, and wd up to the distance of 600 m with the zero speed of wind. In Fig. 12 there is shown the decrease in bullet energy for the two NATO calibres and for the new ones versus the distance up to 500 m. The new calibre has the bigger kinetic energy than 5.56 mm calibre and at the distance of 500 m the difference of almost 200 J is bigger for the new one, despite the fact that 5.56 mm bullet has the higher muzzle velocity but at 450 mm long barrel against 374 mm long barrel for the new cartridge. In Fig. 13 there are shown the 6 mm Scenar bullet paths at the scope of 30 mm above the centre line of the barrel at three different assault rifles aiming at 100 m, 300 m, and 600 m. Also, from Table 4 we can see, that when we want to defeat 3.5 mm steel plate at the range of 600 m, how many kinetic energy Edefeat we need for it. This is common for core bullets made from lead, brass, and steel. The minimal kinetic energy Ewound, necessary to incapacitate individuals, without body armour, is 82 J and the total kinetic energy Etotal for defeat both is stated also in Table 4. New Cartridge Design for Assault Rifle 21
Fig. 11. Bullet energy, velocity, and deviation vs distance for the new cartridge
Fig. 12. Decrease in bullet energy vs distance
Fig. 13. Bullet path vs distance at a scope of 30 mm above the centre line of a barrel for the new cartridge 22 P. Lisý, M. Daniel
Table 4. Kinetic energy for different calibres necessary for defeat individual at 600 m [19]
Edefeat Calibre Ewound Etotal (3.5 mm steel plate) [mm] [J] [J] [J] 5.56 565 82 647 6 638 82 720 6.35 694 82 776 6.5 722 82 804 6.8 776 82 858 7 806 82 888 7.62 910 82 992
3. CONCLUSIONS
Based on the new cartridge design for an automatic assault rifle, the following conclusions can be drawn: 1. Better ballistics performance like 5.56×45 mm NATO and hereby less performance to compare with 7.62×51 mm NATO cartridge. 2. Sufficient precision in accordance with the chosen bullet design, also for the long-range shooting. 3. Sufficient precision due to the smaller barrel vibration. 4. Sufficiently low recoil for the automatic fire than 7.62×51 mm NATO which makes it possible to shoot with the observation fight situation. 5. Reduction of the cartridge mass against 7.62×51 mm NATO but the new cartridge design 6×44 mm has the same sectional density and ballistic coefficient. 6. Need to make both, the new cartridge case and barrel with a chamber for 6×44 mm cartridge and to make real testing. 7. To reach the total kinetic energy necessary for the range of 600 m for the calibre of 6 mm, it is needed to extend a barrel for the new cartridge design. 8. This article is only the small contribution to solve the problem with a new military calibre how it is stated in the article [20]: “The case for a new military calibre is a popular but controversial topic that arouses interest and emotion out of all proportions to the importance of small arms within Army´s.”
New Cartridge Design for Assault Rifle 23
FUNDING
The authors received no financial support for the research, authorship, and/or publication of this article.
REFERENCES
[1] Williams G.A. 2009. “The great calibre conspiracy”. Jane´s Defence Weekly, 11th September, 2009. [2] US Army ARDEC. UK MoD /British Army analysis 2009-2014. Available on the Internet:
[15] Štiavnický Mário, Peter Lisý. 2013. “Influence of Barrel Vibration on the Barrel Muzzle Position at the moment when Bullet Exits Barrel”. Advanced in Military Technology 8 (1) : 89-102. [16] Lisý Peter, Mário Štiavnický. 2014. “Weapon Barrel and its Additional Accessories”. Problemy mechatroniki. Uzbrojenie, lotnictwo, inżynieria bezpieczeństwa - Problems of Mechatronics. Armament, Aviation, Safety Engineering 5 (1) : 9-24. [17] 6.5 Grendel with 90 gr TNT® HP. Available on the Internet: