Recoil

With all the forces being generated to propel the bullet out of the gun there must be forces pushing in the opposite direction of the bullet to satisfy Newton’s third Law of Motion, “For every action there is an equal and opposite reaction”. This is known as recoil.

Under the Law of Conservation of Momentum, the total change in momentum must be zero. For this to be true, there must be an equal amount of momentum pushing back on your shoulder as is pushing the bullet forward. The momentum on your shoulder when a gun a gun kicks back is known as recoil. To calculate the amount of recoil your shoulder receives you can use the following equation for calculating “felt” recoil.

According to the Sporting Arms and Ammunition Manufactures Institute SAAMI Calculating “felt” recoil is determined in the following equation and example: * Note their calculations were not done in SI units and this is a direct quotation from their article so the below calculations are given in standard no SI measurements.

Example from SAAMI

SAAMI also does a great way of relating how recoil is just kinetic energy so that I can be calculated using 1/2 MV^2. This example also shows why recoil is generated when a firearm is discharged. As you can see the larger the mass of the projectile the greater the felt recoil because of momentum. Likewise, a lighter rifle will increase the recoil because the weight of the firearm is in the denominator so the larger of the rifle the weight the smaller the felt recoil. I include this example as it is a great illustration of how recoil works. ALL Credit goes to SAAMI see bibliography for article details.