<P> After modifications (most notably, the charging handle was re-located from under the carrying handle like AR - 10 to the rear of the receiver), the new redesigned rifle was subsequently adopted as the M16 Rifle . "(The M16) was much lighter compared to the M14 it replaced, ultimately allowing Soldiers to carry more ammunition . The air - cooled, gas - operated, magazine - fed assault rifle was made of steel, aluminum alloy and composite plastics, truly cutting - edge for the time . Designed with full and semi-automatic capabilities, the weapon initially did not respond well to wet and dirty conditions, sometimes even jamming in combat . After a few minor modifications, the weapon gained in popularity among troops on the battlefield ." </P> <P> Despite its early failures the M16 proved to be a revolutionary design and stands as the longest continuously serving rifle in American military history . It has been adopted by many U.S. allies and the 5.56 × 45mm NATO cartridge has become not only the NATO standard, but "the standard assault - rifle cartridge in much of the world ." It also led to the development of small - caliber high - velocity service rifles by every major army in the world, including the USSR and People's Republic of China . Today, many small arms experts consider the M16 the standard by which all other assault rifles are judged . </P> <P> During the 1960s other countries would follow the Americans' lead and begin to develop 5.56 × 45mm assault rifles, most notably Germany with the Heckler & Koch HK33 . The HK33 was essentially a smaller 5.56 mm version of the 7.62 × 51mm Heckler & Koch G3 rifle . As one of the first 5.56 mm assault rifles on the market, it would go on to become one of the most widely distributed assault rifles . The HK33 featured a modular design with a wide range of accessories (telescoping butt - stocks, optics, bi-pods, etc .) that could be easily removed and arranged in a variety configurations . </P> <P> The adoption of the M16, the H&K33, and the 5.56 × 45mm cartridge inspired an international trend towards relatively small - sized, lightweight, high - velocity military service cartridges that allow a soldier to carry more ammunition for the same weight compared to the larger and heavier 7.62 × 51mm NATO cartridge . The 5.56 mm cartridge is also much easier to shoot . In 1961 marksmanship testing, the U.S. Army found that 43% of ArmaLite AR - 15 shooters achieved Expert, while only 22% of M - 14 rifle shooters did so . Also, a lower recoil impulse, allows for more controllable automatic weapons fire . </P>

When does a rifle become an assault rifle