The German G3 assault rifle
According to Wikipedia:
The G3 is a 7.62 mm battle rifle developed in the 1950s by the German armament manufacturer Heckler & Koch GmbH (H&K) in collaboration with the Spanish state-owned design and development agency CETME. 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 device 06") prototype assault rifle chambered for the intermediate 7.92 x33mm Kurz cartridge, first with the Gerät 06 model using a roller-locked short recoil mechanism adapted initially 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) or assault rifle) but was not produced in any significant numbers, and the war ended before the first production rifles were completed.