Here, 'assault' is the military term: the final advance over the last 50-100 m to take an objective held by the enemy. An assault rifle is a military rifle which can be fired selectively either semi-automatically or fully automatically. It uses a relatively low-power cartridge and is generally designed for low-cost production, light weight, and use by minimally trained personnel. In the US, all these are subject to the National Firearms Act of 1934, and to state laws on automatic weapons. However, some state and federal laws also define many other semiautomatic rifles as "assault rifles".
A military rifle intended purely for one-man operation and equipped to provide both semiautomatic or full-automatic fire by means of a selector switch or other fire-control device. Today's assault rifles are typified by the Soviet AK 47 and the U. S. M 16. They are chambered for an intermediate cartridge, have barrels under 20 inches, make extensive use of plastics and stampings, use gas operation and locked breeches, have magazine capacities of 20 to 30 rounds, weigh from six to 10 pounds and are quite compact.
any of the automatic rifles or semiautomatic rifles with large magazines designed for military use