Previously in Operating Systems 101, we covered the simple, inexpensive principle of blowback, and the reliable principle of short-recoil. Both of these mechanisms together form the foundations of almost all automatic handguns in common use today, but what about rifles? Well, the most common mechanism for rifles is the method of gas operation, developed by legendary Utahn Mormon gun wizard John Moses Browning. Browning observed that the gases coming from the muzzle of a rifle could influence objects around it, such as tall grass. Through tireless experimentation, Browning found he could harness this gas, and the principle of gas operation was born.

• Gas operation: The principle by which the pressurized propellant gases of a firearm are tapped from the barrel and used as the primary motive power for an automatic mechanism.

Gas operation differs from some other forms of operation (which we’ll be sure to discuss later) that also tap propellant gases in that it is the tapped gas pressure that provides the primary power for the automatic mechanism. Weapons that use gas to unlock a mechanism but not to cycle it therefore are not normally categorized as “gas operated”.

To illustrate how the principle works in practice, we will take a look at the video below, starting at 4:47 to see how the gas-operation of the M1 Garand rifle works:

Gas operation is commonly used for military rifles, as it is a robust, reliable mechanism that allows for consistent accuracy over the weapon’s lifespan (as unlike short-recoil operation, the barrel remains fixed to the receiver), and can be made very lightweight and simple. Its popularity is due to the fact that it has few downsides, but those it does have include needing to mount a device to the barrel itself (preventing true isolation of the barrel) to utilize the gas, as well as potential vulnerabilities to heat and, in some incarnations, fouling.