AR-15 Direct Impingement gas system

by Erik  

The AR-15 operates using a gas blow back system. This means that as the weapon is fired, some of the gas from a fired cartridge is recycled before leaving the barrel. It travels down a tube which blows the gas back into the receiver to eject the empty cartridge. It is called a cycle. This all happens in less that a second and is vital the weapon operating correctly.

The traditional gas system explained above is called Direct Impingement or DI for short. Most moderately priced AR-15s will use a DI gas system. The complete operation is illustrated below:

The gas system on an AR-15 can be adjusted for various situations or combinations of equipment and accessories. This is usually done with a special upper receiver or gas block. Some gas blocks are user adjustable via a screw or knob. This allows the amount of gas to be adjusted for use with suppressors or different barrel lengths. Shown below is a good example of tuning a gas block to allow the weapon to cycle properly:

There is also another article which discusses the use of piston operated AR-15 gas systems.

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