The StG 45(M) (Sturmgewehr 45 literally "storm rifle" or "assault rifle 1945") sometimes referred to as the MP 45(M), was a prototype assault rifle developed by Mauser for the Wehrmacht at the end of World War II, using an innovative roller-delayed blowback operating system. It fired the 7.92×33mm Kurz (or "Pistolenpatrone 7.9mm) intermediate cartridge at a cyclic rate of around 450 rounds per minute.
he origin of this rifle can be traced back to the final years of World War II when Mauser engineers at the Light Weapon Development Group (Abteilung 37) at Oberndorf am Neckar designed the MKb Gerät 06 (Maschinenkarabiner Gerät 06 or "machine carbine instrument 06") prototype assault rifle chambered for the intermediate 7.92×33mm Kurz cartridge, first with the Gerät 06 model using a roller-locked short recoil mechanism originally adapted from the MG 42 machine gun, but with a fixed barrel and conventional gas-actuated piston rod. It was realized that with careful attention to the mechanical ratios, the gas system could be omitted. The resultant weapon, the Gerät 06H (the "H" suffix is an abbreviation for halbverriegelt or "half-locked") was assigned the designation StG 45(M) (Sturmgewehr 45(M)).
However, the design first suffered from an inherent flaw: Without a gas vent (as used by gas-operated autoloading weapons) to relieve combustion pressure before the projectile could leave the barrel, the gas pressure from the fired cartridge would press the case against the loading chamber walls, resulting in jams. As a result, gas relief flutes were cut into the chamber, allowing the combustion gas to stream past the cartridge case and thus relieving the pressure. During the process, the case would be scorched in a manner which was characteristic for later Heckler & Koch blowback-operated weapons, which used the same principle.
The StG 45(M) was intended to replace the Sturmgewehr 44 assault rifle, because the latter was rather expensive and time-consuming to produce. Compared to the StG44's cost of 70 Reichsmarks, the StG45(M)'s calculated cost was 45 Reichsmarks. Parts for only 30 complete rifles were produced before the war ended.