StG 45 ( M ) 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 . Overview . The 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 . While the StG45 ( M ) was intended to use the same 30 - round magazine as its predecessor , the rifle is commonly pictured with the 10 - round magazine designed for the " Volkssturmgewehr " . The shorter magazine was used by Mauser engineers during testing , as its lower profile was easier to use when test - firing at the Mauser facility range . Post - World War II developments . The German technicians involved in developing the " Sturmgewehr " 45 continued their research in France at CEAM . The StG45 mechanism was modified by Ludwig Vorgrimler and Theodor Löffler at the Mulhouse facility between 1946 and 1949 . Three versions were made , chambered in . 30 Carbine , 7 . 92×33mm Kurz as well as the 7 . 65×35mm cartridge developed by Cartoucherie de Valence and adopted in 1948 . A 7 . 5×38mm cartridge using a partial aluminium bullet was abandoned in 1947 . Löffler ' s design , designated the " Carabine Mitrailleuse Modèle " 1950 , was retained for trials among 12 different prototypes designed by CEAM , MAC , and MAS . Vorgrimler later went to work at CETME in Spain and developed the line of CETME automatic rifles . Germany eventually purchased the license for the CETME design and manufactured the Heckler & Koch G3 as well as an entire line of weapons built on the same system , one of the most famous being the MP5 . A few other post - World War II weapons used the roller - delayed locking system , such as the SIG SG 510 .