.308 / 7.62 NATO / HK 91a3 / HK G3/ PTR 91/CETME. Slow motion delayed Roller-lock Blowback system. Different from direct impingement, piston or direct blowback. The action counteracts the recoil and the compensator eliminates the barrel jump with an ingenious ejection system modeled from the Sturmgewehr but evolved and adopted by many countries around the world in the form of the HK G3 Battle Rifle.