Telescoping bolt

Though technically a different, distinct concept, nearly all telescoping bolt submachine guns use a magazine located in the pistol grip used to hold and fire the weapon.

These pistols, starting with the FN M1900 and to continuing to the present, often feature a slide, which acts as both a barrel shroud and the bolt.

[2] One of the earliest submachine gun known to use the telescoping bolt concept was the Italian Armaguerra OG-43, followed by the OG-44, designed by Giovanni Oliani during the later stages of the Second World War.

[3] The first production model submachine gun using a telescoping bolt was the Czechoslovak Cz 23 aka Sa.23 or vz.48b series, first produced in 1948.

As the image diagrams demonstrate, the basic concept of a telescoping bolt with the magazine well in the handgrip produces significantly more compact weapons.

Two 9×19mm submachine guns with 250 mm (10 inch) barrels, an Uzi (with a telescoping bolt) and MP40 (without), showing the compactness a telescoping mechanism allows
Internal mechanisms of the above submachine guns. Barrels are blue, bolts are green.