Piston Rods
In addition, the carbine was the first successful semi-auto to use a tappet (short piston) operated, short-stroke gas system. High pressure gas is tapped from the barrel close to the chamber and used to drive a small gas piston a short distance (less than 0.25") at a very high velocity. When fired, the carbine’s tiny gas piston slaps the inner face of the operating slide hard enough to drive it rearward, unlock the bolt and extract the fired cartridge case from the chamber.
Then, a return spring on the slide drives it forward to strip a fresh round from the magazine, chamber it, lock the bolt in battery and finally depress the little piston in its gas block again. The major advantage of the carbine’s tappet gas system was a lighter overall weight for the weapon (about 5.5 lbs loaded) achieved through shortening the action’s operating parts. The modern SCAR uses the same short-tappet gas system.