ASSAULT RIFLES AND THEIR AMMUNITION:

HISTORY AND PROSPECTS

Revised 21/10/2006



© Anthony G Williams



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 military rifle, capable of controlled, fully-automatic fire from the shoulder, with an effective range of at least 300 metres".

This has some clear implications for the ammunition such weapons are chambered for. First, it excludes all weapons designed around pistol cartridges (i.e. sub-machine guns - SMGs) as they only generate around 500 joules muzzle energy and cannot meet the range requirement. Second, it excludes the traditional "full power" military rifle/MG cartridges such as the .303", the .30-06, the 7.92x57 and the 7.62x51 NATO (typically firing 10-12g bullets at 750-850 m/s, and developing around 3,000-4,000 joules), as these are so powerful that their recoil is uncontrollable in fully-automatic fire from the shoulder. Assault rifles therefore need to be designed around a cartridge intermediate in power between pistol and full-power rifle rounds; in practice, approximately in the 1,250-2,500j range depending on the calibre.

Attempts have been made to extend the effective range of SMGs by developing more powerful cartridges for them. However, there is a limit to the degree to which this can be achieved as the basic API blowback mechanism used by most SMGs is not suited to high-powered ammunition. Attempts have also been made to design automatic rifles around full-power cartridges, perhaps the most famous example being the German FG 42 paratroop rifle in 7.92x57. Some of the early rifles in 7.62x51 NATO, such as the American M14, were also capable of fully automatic fire, but the recoil problem made them incapable of accurate fire on full-auto and they cannot be classified as assault rifles.

There have been two contrasting approaches to the design of a suitable intermediate cartridge with the appropriate compromise between long range and light recoil. One is to retain the same 7.6-7.9mm calibre as the full-power 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 while retaining the same, or a higher, velocity (reduced calibre, or RCAR rounds).

FCAR rounds score well in the traditional methods of measuring stopping power (which are 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.

A decision to reduce the calibre raises the immediate question; by how much? At the large end of the RCAR scale (7mm), bullet weight and muzzle velocity can be much the same as in the FCAR cartridges, but the better ballistic coefficient due to the longer and more slender bullet will reduce velocity loss and improve long-range performance. However, there is potentially some loss in stopping power. As the calibre decreases, so the recoil and the ammunition weight become lighter and the velocity can be higher, thereby flattening the trajectory; all good things. The downside is that the stopping power becomes more controversial (relying on velocity rather than calibre and bullet mass; which according to combat reports sometimes works, sometimes doesn't) and the long-range performance begins to decrease again as small-calibre bullets generally have poorer sectional density ratios, and thereby ballistic coefficients, than large-calibre ones.

Different nations have made different choices in developing assault rifles, and the purpose of this article is to describe and analyse them in order to examine the future prospects for this type of weapon.

Development before World War 2

The elements of an assault rifle were in place surprisingly early in the history of automatic weapons. Self-loading rifles were developed before the end of the 19th Century and the first selective fire (semi or full auto) rifle using a medium-power cartridge was probably the Italian 6.5mm Cei-Rigotti, developed between 1900 and 1905, but this was not adopted. Mannlicher introduced their m/1901 carbine in a purpose-designed 7.65x32 calibre, but the loading was relatively weak and it also was not adopted.

Small-calibre rifle cartridges were also in use or under development for military purposes. The USN's 6mm Lee of 1895 is probably the best known, but the curious 5.2mm Mondragon of 1894 was also made (the odd shape resulting from an internal piston to give the bullet an initial kick up the barrel) and the 5mm Sturtevant was being developed towards the end of WW1.