40mm antiaircraft gun. Description and operation

Washington, D.C.: Navy department bureau of ordnance. 1943.Ordnance Pamphlet No. 820 provides a description of the construction and operation of the 40mm Machine Gun Mechanism,
and descriptions of the gun barrel and sight. It also includes operating instructions and instructions for the care and maintenance
of the gun.
40mm machine gun mechanism - Mark 1, Mark 2, Mark 1 Mod. 1, Mark 2, Mod. 1. 40mm gun barrel