Recoil
The rearward push you feel when the rifle fires. Heavier rifles and muzzle brakes both reduce felt recoil.
Recoil is conservation of momentum applied to a bullet leaving a barrel. The bullet goes forward; an equivalent impulse pushes the rifle backward. Felt recoil — how hard the gun hits your shoulder — is a function of bullet weight, velocity, rifle weight, and gas energy.
Magnums punish; .22 LR is delightful. Most of long-range training is about managing the rifle’s behavior under recoil so you can spot your own impacts without losing the target.