(under the class definition) Devices having adjustable means
to compensate for the distance between the face of the locked bolt or breech block of a firearm and some specified point in the chamber.
(1) Note. With guns designed for rimless, bottlenecked cartridges, head space is the space between the bolt face and specified point on the shoulder of the chamber; with guns using rimmed cartridges, the head space between the bolt face and the ridge or abutment in the chamber against which the rim rests; and with guns using rimless straight-case cartridges, the space between the bolt face and the ridge or point in the chamber where the mouth of the cartridge case rests.
