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).