Recoil operation: Encyclopedia II - Recoil operation - How they work

Recoil operation - How they work

When a projectile is accelerated down the barrel of a firearm, all or a portion of the firearm will begin to move in the opposite direction, as required for conservation of momentum, according to the formula:

:Bullet mass * bullet velocity = recoiling mass * recoil velocity

In non-recoil-operated firearms, it is generally the entire firearm that recoils. In recoil-operated firearms, however, only a portion of the firearm is allowed to recoil, while inertia holds another portion motionless relative to the recoiling mass. These two masses are coupled by a spring, which is compressed by the movement, and which serves to return the different masses to their original position.

Since there is a minimum momentum required to operate any given recoil-operated firearm's action, the cartridge must generate sufficient recoil to provide this momentum. Since cutting the mass of the bullet in half requires doubling its velocity to conserve momentum, thus quadrupling the kinetic energy that is required for the bullet, the kinetic energy requirements are lessened and recoil-operated firearms tend to work best with more massive projectiles in a given cartridge. Also, since most recoil-operated fireams directly use the recoiling parts to perform desired functions, there is often a maximum recoil momentum beyond which reliability will suffer or damage may occur to the action. Likewise, there is a minimum recoil momentum below which operation of the gun will likewise not be reliable. Recoil operated firearms therefore tend to work best when using a cartridge with a grain size (mass) near where the gun's action was originally optimized in terms of momentum. For example, the M1911 was initially designed around a 230 grain bullet, and, although there is a fairly-wide range over which different grain bullets may still operate ok, the optimal operation will nonetheless occur around a 230 grain bullet size, for standard factory springs.

The different implementations of recoil operated designs are broadly categorized by how the parts move under recoil. The categories are long recoil, short recoil, and inertia operated.

Adapted from the Wikipedia article "How they work", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki