upper
An upper is the upper half of a two-piece receiver, usually housing the bolt assembly and stock assembly. Most shooters are familiar with the concept of upper and lower receivers through the AR platform, but many other firearms have uppers and lowers, from the FAL battle rifle to the MAC submachine gun. The upper is often (but not always) the unserialized portion of the gun, meaning it is legally just machine parts and can be bought and sold without interference.
See also: AR upper.
See also: AR upper.
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