The StG 45(M) (the M standing for Mauser, the company that built the weapon) was developed with a ten-round box magazine, but could also use the same thirty-round magazine that was used in its predecessor, the StG 44, on which the StG 45(M) was based. It fired the relatively new 7.92×33mm Kurz Cartridge and the rate of fire was about 400 rounds per minute.
The StG 45(M) was originally intended to supplement, and eventually, replace the earlier StG 44. The latter was rather heavy, which is a reason why a replacement was constructed. Another reason was that the StG 44 cost seventy Reichsmarks, while its intended replacement, the StG 45(M), cost only around forty-five Reichsmarks. The StG 45(M) was also simpler than the StG 44, and it used less parts. Due to the rapid push of Allied forces into Germany, the weapon was never put into service. The design of the StG 45(M) later led to the development of the HK21 machine gun and HK G3 rifle, as well as later weapons.