When you fire a gun, the recoil velocity refers to how quickly the weapon kicks back at you. The gun recoils because of the conservation of momentum. Since the gun and the bullet both start at rest, the force that pushes the bullet out of the gun also pushes it back in the opposite direction. In order to calculate the recoil velocity, you need to know the speed at which the bullet is shot and the weight of the gun and bullet.
Determine the weight of the gun and the weight of the bullet using a scale. For example, a gun may weight nine pounds and the bullet may weigh 0.1 pounds.
Check the gun specifications to determine the initial velocity of the bullet. For example, the gun may shoot the bullet at a speed of 1,000 feet per second.
Multiply the weight of the bullet by the initial velocity to find the momentum of the bullet. In this example, you would multiply 0.1 pounds by 1,000 feet per second to get 100 pound feet per second.
Divide the result from step 3 by the weight of the gun to calculate the recoil velocity of the gun. Finishing this example, you would divide 100 pound feet per second by 9 pounds to find the recoil velocity is about 11.1 feet per second.