Assault Rifles and Their Ammunition: History and Prospects
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1 ASSAULT RIFLES AND THEIR AMMUNITION: HISTORY AND PROSPECTS © Anthony G Williams, Editor IHS Jane's Weapons: Ammunition Last amended November 2016 (major re-write) Introduction First, I need to define what I mean by an "assault rifle", as there are various definitions around. The one I use is: "A standard military rifle, capable of controlled, fully-automatic fire from the shoulder, with an effective range of at least 300 metres". This raises various questions, including: "what do you mean by effective range?". This is sometimes held to be where there is a 50% chance of the average soldier hitting a human target with a single aimed shot, but in more general terms could be expressed as the range within which aimed fire is likely to hit or suppress the enemy – suppression meaning to deter the enemy from effectively fighting back or moving position, something which is achieved by near misses. Another obvious question is: "what do you mean by controlled?". There is no agreed definition, but the implication is that for automatic fire to be useful, the average infantryman should be able to keep short bursts of fire on a human target at short range, with a useful percentage of the bullets scoring hits. Controllability is affected by gun design – the shape of the stock, the type of gun action, the use of muzzle brakes or suppressors, and especially the weight of the gun – but the above definition of "assault rifle" has some clear implications for the ammunition such weapons are chambered for. First, it excludes weapons designed around pistol cartridges (i.e. machine pistols and sub-machine guns - SMGs) as they only generate around 500 joules (J) muzzle energy (ME) and cannot meet the range requirement. Second, it excludes the traditional "full power" (FP) military rifle/MG cartridges such as the .303" (7.7 x 56R) British, the .30-06 (7.62 x 63) US, the 7.92 x 57 German, the 7.62 x 54R Russian and the 7.62 x 51 NATO (typically firing 10-12 g bullets at muzzle velocities (MV) of 750- 850 m/s and developing around 3,000-4,000 J), as these are so powerful that the recoil they generate is virtually uncontrollable by the average soldier using fully- automatic rifle fire from the shoulder. Ammunition developing MEs and recoil somewhere between the SMG and FP types is needed (ME and recoil are separate calculations, but broadly linked). The history of assault rifles is very much focused on the development of the ammunition which they use. It took some time for suitable ammunition to become available. Early efforts towards light automatic weapons saw pistols such as the Mauser C96 (7.63 x 25) and P08 Luger (9 x 19 Parabellum) modified to produce carbine derivatives with detachable stocks, usually only capable of semi-automatic fire but a few with a burst-fire option. These were relatively fragile and expensive to make, however, so the future in short- range automatics lay with the much simpler blowback SMG. The first of these in 2 service (if you discount the curious twin-barrel Villar Perosa) was the Bergman MP18 in 9 x 19, which was the ancestor of the MP 38/40, the Sten Gun, the PPSh and so on. An honourable mention also to the Thompson, developed separately in the USA from 1916 onwards for their .45 Auto (11.5 x 23) cartridge. An oddity was the Pedersen Device of 1918, which replaced the bolt in the US Springfield Rifle with a semi-automatic mechanism to fire small .30 cal (7.62 x 20) pistol-type rounds developing less than 400 J; it was never used in anger. Attempts to improve the power and range of the SMGs, such as the development of the .45 Remington-Thomson in the experimental Model 1923 Thompson SMG (which used a very powerful loading developing almost three times the ME of the .45 Auto) and the use of the 9 x 25 Mauser round in the 1930s Solothurn S1-100 and Hungarian Kiraly 39M and 43M SMGs (which saw some service), did not catch on. There is a limit to the degree to which the performance of such weapons can be increased as their large-calibre, relatively light and round-nosed bullets lose velocity quickly. Also, the blowback operating system used by most SMGs is not suited to high-powered ammunition, although the Kiraly and Thompson M1923 had more sophisticated mechanisms. .30 Pedersen (7.65 x 20), .30 Mauser (7.63 x 25), 9 x 19 Parabellum, 9 x 25 Mauser, .45 Auto (11.5 x 23), .45 Remington-Thompson (11.5 x 26), 5.7 x 28 FN, 4.6 x 30 HK, 5.8 x 21 DAP-92. More recently, small-calibre high-velocity PDW ammunition has emerged (described in more detail in a separate article1). The FN 5.7 x 28 has achieved some sales, in both the Five-seveN pistol and the P90 SMG, as has the rival HK 4.6 x 30 in the MP7. However, despite their improved range performance, these cartridges still only develop around 500 J so don't qualify as assault rifle ammunition. The Chinese 5.8 x 21 DAP-92 is even less powerful. At the other end of the power scale there were many attempts from the beginning of the 20th century to increase the firepower of the FP infantry rifle by replacing its manual bolt-action with a self-loading mechanism (some of them shown below). However, such weapons did not enter general service as standard infantry rifles until the US M1 Garand in 1937. 1 http://quarryhs.co.uk/PDWs.htm 3 Some early semi-automatic rifles, from top to bottom: 1918 .303 Farquhar Hill; 1909 Mondragon (7.92 mm); 1917 MAT Mk 1917; 1929 Czech Brno Z.H.29 (photo taken at MoD Defence Academy, Shrivenham) Attempts to make such weapons fully automatic ran into difficulties due to their heavy recoil. Perhaps the most successful examples were the WW2 German FG 42 paratroop rifle in 7.9 x 57 and the postwar Swiss Stgw.57 in 7.5 x 55, but these were significantly heavier than contemporary rifles, the weight helping to absorb the recoil. This is even more true of the US Browning Automatic Rifle (BAR) in .30-06 which was even heavier, weighing about twice as much as a "standard military rifle"; its low rate of fire also helped controllability. Some of the early rifles in 7.62 x 51 NATO, such as the US M14, German G3 and some versions of the FN FAL, were also capable of fully automatic fire, but the recoil problem made them more or less uncontrollable so they cannot be classified as assault rifles. Assault rifles therefore need to be designed around a cartridge intermediate in ME between SMG and FP rifle rounds; in practice, approximately in the 1,250-2,500 J range depending on the calibre. There have been two contrasting approaches to the design of a suitable cartridge with the appropriate compromise between long range and light recoil. One is to retain the same 7.5-8 mm calibre as the FP round, but with a shorter cartridge case firing a lighter bullet at a lower muzzle velocity (lets call these "full calibre assault rifle", or FCAR, rounds). The other is to reduce the calibre 4 while retaining the same, or a higher, velocity (reduced calibre, or RCAR rounds). FCAR rounds score well in the traditional methods of measuring barrier penetration and terminal effectiveness (dominated by calibre and bullet weight) and also by being less affected by the bullets striking foliage etc on their way to the target. However, they have a relatively steep trajectory and a rapid velocity loss due to the short, fat bullets, which quickly reduces their effectiveness at long range. The full-power 7.9 x 57, 7.5 x 55, .30-06 and 7.62 x 51, shown next to the 7.62 x 39 and 5.56 x 45 which are the most common FCAR and RCAR rounds respectively A decision to reduce the calibre raises the immediate question; by how much? At the large end of the RCAR scale (7 mm), bullet weight and MV can be much the same as in the FCAR cartridges, but the better ballistic coefficient (BC) due to the longer and more slender bullet will reduce velocity loss and improve long-range performance. As the calibre decreases, so the recoil and the ammunition weight become lighter and the MV can be higher, thereby flattening the trajectory; all good things. The downside is that barrier penetration may be reduced and stopping power becomes more controversial (relying on velocity and rapid bullet yaw on impact rather than calibre and bullet mass; which according to combat reports sometimes works, sometimes doesn't). The long-range performance also begins to decrease as small-calibre bullets generally have BCs which are inferior to large-calibre ones. Different nations have made different choices in developing assault rifles, and the purpose of this article is to describe and explain them in order to examine the future prospects for this type of weapon. 5 Developments up to 1918 The elements of an assault rifle were in place surprisingly early in the history of automatic weapons. The first selective fire (semi or full auto) rifle was probably the Italian Cei-Rigotti, developed between 1900 and 1905 around a 6.5 mm cartridge with less power and recoil than the usual 7.5-8 mm FP types, but this was not adopted.