The US Army uses two distinct families of weapons in 5.56 x 45 mm calibre: the M16 rifle and the derivative M4 carbine form one group, the M249 Squad Automatic Weapon the other.

美国陆军使用两种截然不同的5.56毫米口径木仓族：一种是M16步木仓以及其派生出来的M4卡宾木仓，另一种是M249班用机木仓。

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The Bushmaster M4 Types Carbine, a semiautomatic rifle, uses a 20 or 30-round magazine.

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