Germany produced the first successful rifle that meets all of the modern criteria, the Sturmgewehr 44. Introduced in 1944; too late to have a serious effect on the war, the Stg 44 was a selective fire weapon that fired a reduced power cartridge. It weighed no more than a standard rifle, and incorporated a straight line stock to reduce muzzle climb. A thirty round box magazine was easily replaced when empty. The cartridge was only 66% as long as the standard rifle cartridge, with a bullet only 60% of the standard weight and a powder charge of 50%. This allowed a higher rate of fire while maintaining decent control on the weapon. It also allowed the soldier to carry a larger amount of ammunition, and saved money in manufacture and resources.
All current assault rifles are descended from the Stgw 44. Differences in the operating systems are really only details; efforts to make the basic idea slightly more efficient. The most important advances in assault rifles were made when effective small caliber ammunition was developed. Most countries now use either some version of the 5.56 NATO round; or the (former) Soviet 5.45 x 45mm. In the U.S. Army, the basic combat load has risen from 80 rounds in WW II (4.8 pounds/2.2Kg weight), to 210 rounds today (5.5 pounds/2.5Kg weight). The use of composite materiels also brought the weight of the rifle down, from about 9 pounds to 6.5 pounds (4.1 to 2.9Kg).
The current assault rifle is not the final answer to the ground combat question, though. Since the defenders also use select fire rifles, the balance between defense and offense remains. New technology may provide advances that will swing the pendulum again.
http://www.sturmgewehr.com/ This site provides discussion boards and classifieds related to assault rifles
http://www.fnfal.com/falfiles/combat2.ht... site that extols the triumphs of the FN FAL.
http://www.wwa.com/~dvelleux/m14rifle.ht... to the M-14, with a wealth of links.
