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Parallel with submachine gun development during the interwar period was the thinking that would evolve into the assault rifle: Factions within several of the military establishments knew that most effective military action with shoulder fired weapons took place within 400 meters. A medium powered cartridge (MPC) would be sufficient at this range, cheaper to produce, enable a soldier to carry more ammunition and allow better control in automatic mode.
As early as 1909 the British experimented with a slightly lighter cartridge for their service rifle than the .303 i.e. the .276 (7mm) Enfield but World War I interrupted this line of thinking. When in the 30s the US Army began developmental trials of a self loading rifle they too chose a lighter cartridge, the .276 Pedersen but fore seeing coming hostilities the 30-06 was retained. Though both these developments showed an interest in lighter rounds neither would fit the category of a MPC.
Concurrently the 30s saw Switzerland, Finland, Germany and Russia investigating MPCs. The Russians began development of the 7.62X39mm but dropped it in 1939. In 1935 the Germans fixed on the 7.92X33mm Kurz and by 1940-41 Haenel had produced the Maschinenkarabiner 42(H) or MKb42(H). This straight stocked, gas operated, weapon made extensive use of steel stampings and spot weldings. Shortly there after Walther produced its entry, the Maschinenkarabiner 42(W) but the army didnt like its more complicated turn bolt design and eventually dropped it from consideration.
Eight thousand of the Haenel MKb42(H) were manufactured and tested on the Russian Front from November of 42 until April of 43. A few fell into Russian hands reviving their interest in the concept and by 1943 they had developed a MPC of their own, the 7.62X39mm 1943.
Combat lessons learned during the trials of the MKb42(H) formed the basis for modifications that brought about the emergence of the grandfather of all assault rifles i.e. the Sturmgewehr 44 (MP43, MP43/1, MP44, StG44). First deliveries to the German army were in July 1943 and they were produced until 1945. In the field the troops felt that (the weapons are) especially suited for patrol, raiding and attack.
Another tactical advantage of assault rifles seldom mentioned is that they encourage general area suppressive fire by riflemen. In World War II many US infantrymen didnt fire if they didnt have a target leaving suppressive fire to the machine guns.
After the war the Soviet Union fielded the famous AK47 in 7.62X39mm. Reportedly thirty-five million of these rugged, gas operated weapons have been manufactured. Originally they were produced with a receiver machined from solid steel but in 1959 to save money and weight the AKM was deployed using stampings.
During this same period NATO wanted to adopt a common rifle and cartridge. Although the United States paid lip service to the assault rifle idea, it forced NATO to adopt the 7.62X51; a full power round half an inch shorter than the 30-06 but with almost identical ballistics. The US adopted the M14 and the NATO countries the FN rifle, neither of which could be termed an assault rifles.
The US army did attempt a number of experimental cartridges to increase the fire power of the M14. One such round fired flechettes and another had two 7.62 bullets loaded follow-on style, to disperse in flight. Both were unsuccessful.
Eugene Stoner, working for Fairchild Engine and Airplane Company, was, at the same time, hard at work on a rifle called the Armalite (AR10 and AR15) and completed the weapon to army specifications in 1956. His first design was for a full powered cartridge but eventually he settled on a .223 (5.56mm) round specifically designed for his rifle. Gas operated, it was highly reliable and had such low recoil that one demonstrator fired it full auto holding the butt on his chin.
Colt purchased a license to manufacture the rifle in 1959 and in 1963 Secretary of Defense MacNamara forced the army to adopt and field the rifle in Vietnam. After an unforgivable fiasco of malfunctions and modifications the rifle finally emerged as a reliable weapon, and evolved as the present day M16A2/A3 and its variants.
The M16 was first designed to fire a spitzer (pointed) boatailed bullet at 3250 fps, in 1984 this was changed to the 5.56X45 NATO--at 3100 fps. The latter bullet has a mild steel penetrator tip in front of the lead core giving it better penetration at its extreme ranges but much less knock down power than the original loading. I have to say it looks like a bad trade off.
In 1974 the Russians brought out an interim design; the AK74. It fired a new cartridge, the 5.45X39mm Soviet. The bullet has a spitzer configuration with an air space in the tip to make it unstable upon contact with flesh and therefore very lethal. By all accounts that came out of Afghanistan, they succeeded. For the most part the AK74 is a small caliber model of the AKM except for a slightly modified operation system, plastic magazine and more efficient muzzle break. -- Peter38