A schematic of the roller-delayed blowback mechanism used in the MP5 submachine gun. This system had its origins in the late-war StG 45(M) assault rifle prototype.
Roller-delayed blowback was first used in the experimental MG 42 derivative MG 42V and the 1945 Mauser StG 45 prototypes. Roller-delayed blowback operation differs from roller-locked recoil operation as seen in the MG 42. Unlike the MG 42, in roller-delayed blowback the barrel is fixed and does not recoil. As the bolt head is driven rearward, rollers on the sides of the bolt are driven inward against a tapered bolt carrier extension. This forces the bolt carrier rearward at a much greater velocity and delays movement of the bolt head. The primary advantage of roller-delayed blowback is the simplicity of the design compared to gas or recoil operation.
After the war, former Mauser technicians Ludwig Vorgrimler and Theodor Löffler perfected this mechanism between 1946 and 1950 while working for the French Centre d'Etudes et d'Armament de Mulhouse (CEAM). The first full-scale production rifle to utilize roller-delay was the Spanish CETME followed by the Swiss Sturmgewehr 57, and the Heckler & Koch G3 rifle. The MP5 submachine gun is the most common weapon in service worldwide still using this system. The P9 pistol also uses roller-delayed blowback; however, the Czech vz. 52 is roller-locked.