was a roller-delayed blowback-operated firearm with a semi-rigid locking mechanism designed to retard the rearward movement of the bolt. This delay was achieved by artificially increasing the inertia of the bolt by using an angular, interposed transmission system, installed symmetrically to the bore axis, with two cylindrical rollers acting as transmission elements against a movable locking piece which drives the heavy bolt carrier. The two-piece bolt assembly consists of a bolt head, which contains the aforementioned rollers, and a supporting locking piece and bolt carrier. During the "unlocking" sequence, the bolt head receives the recoil impulse from the ignited cartridge and exerts rearward pressure against the rollers, seated in recesses in the barrel extension. The rollers are driven inward against angled ramps of the barrel extension and interact with the wedge-shaped locking piece, projecting it backwards. Thus a transmission ratio is maintained (as long as the rollers move on the inclined surfaces of the barrel extension and locking piece) of the bolt carrier and locking piece relative to the bolt head; the bolt carrier travels backwards considerably faster than the bolt head, ensuring a safe drop of pressure within the barrel prior to extraction. Extraction is carried-out under relatively high pressure. The primary advantage of roller-delayed blowback is the simplicity of the design compared to gas or recoil operation. It is unknown whether the MG 45/42V had longitudinal gas relief flutes in the chamber designed to help free the bloated cartridge casing from the chamber walls during extraction. Fluting the end of the chamber provides pressure equalization between the front outer surface of the cartridge case and its interior and thus ensures extraction without tearing the tapering part of the case of bottle necked cartridges. Metall- und Lackwarenfabrik Johannes Großfuß (Metal and lacquer ware factory Johannes Großfuß) chief designer Werner Gruner stated that gas relief flutes were present, his colleague Hans-Joachim Kaltmann denied this. Tests First tests were undertaken in June 1944, but development dragged on and eventually only ten machine guns were built. During tests a MG 45/42V fired 120,000 rounds in succession at a cyclic rate of fire around 1,350-1,800 rounds per minute. See also Barnitzke machine gun MG 60—post World War II derivative References 7.92×57mm Mauser machine guns General-purpose machine guns Machine guns of Germany Medium machine guns Roller-delayed blowback firearms Trial and research firearms of Germany World War II infantry weapons of Germany World War II