Semi Automatic

This page is dedicatd to the firearms action type of "Semi Automatic".

There are many types of semi automatics. The designs listed below are some of them until all are listed these are only a few.

Blow back action
This style is where the pressure of the fired powder blows the bolt or slide back cycling the weapon. It kicks the empty casing out and pushes the new one up into the chamber, when the slide or bolt goes back it cocks the hammer so that you may fire again.

Gas Piston
In a gas-operated mechanism, a portion of the combustion gases propelling the bullet within the barrel are diverted and used to unlock the bolt and cycle the action rearward. In most designs the gas port is located relatively close to the muzzle, which ensures that chamber pressure has dropped to a safe level before the breech is opened. There are two primary mechanisms used to achieve this. The first method, called a "gas piston," uses the high pressure gas ported from the barrel to drive an enclosed piston back against an operating rod or linkage (they are often one piece), which in turn unlocks the bolt and drives it rearward, ejecting the spent case and cocking the hammer or striker spring. The bolt moving rearward also compresses a strong recoil spring which subsequently returns the bolt forward, stripping a fresh round from the weapon's magazine and forcing it into the chamber in the process. The AK-47/74 uses this piston-based mechanism.

The second method of operation, called direct impingement , is somewhat simplified. Here, the tube carrying the high pressure gas ported from the barrel emerges inside the action of the rifle, where it mates up with a "gas key" which is integral to the bolt carrier. Thus, the bolt carrier itself functions as a piston as in the French MAS-49 and 49-56 rifles. The AR-15 and its military versions, the M16 and M4 Carbine, are the most common and well-known weapons which utilize this system.