Need help with the causes of recoil.

[Hookeye]

Semi automatic weapons absorb or re-utilize a good bit of the recoil energy to function the weapon. An AR15 has a nice big spring being pushed back by a relatively heavy bolt carrier group. A 30-30 transmits the recoil energy into a fixed breech face which pushes it into the shoulder.

It was my understanding that the semi auto (if of same weight as fixed breech system) has the same recoil, but due to the recoil being distributed over a longer period it is perceived to be less.