Telescoping bolt

A weapon with a telescoping bolt (also known as an overhung bolt) is one with a bolt which telescopes over, that is, wraps around and past, the breech end of the barrel. This feature reduces the required length of a weapon such as a submachine gun significantly, and it allows rifle designs to be balanced around the pistol grip in a way that gives "pointability" similar to a pistol's.

While it would be simpler and easier to shorten the bolt to fit completely behind the breech, the bolt must have a certain amount of mass in order to operate reliably with a given caliber. The telescoping bolt moves some of that mass forward of the bolt face, resulting in a bolt which is longer overall, but is shorter behind the bolt face.

Though technically a different, distinct concept, nearly all telescoping bolt submachine guns do use an ammunition magazine located in the pistol grip which is used to hold the weapon.

History

The telescoping bolt concept first appeared on semi-automatic handguns designed by John Browning, such as the M1911-series pistol produced for the U.S. Army. These pistols feature a slide, which acts as both a barrel shroud and the bolt. This allowed Browning to design compact pistols for high-powered cartridges.