dang, everyone beat me too it :D
Tell your bolt guy to think about it this way. If you take the same weight, and add the same amount of force, you get the same energy pushing against your shoulder (same caliber, same weight gun, same recoil). The difference between a semi and a bolt, is that the semi has a build in shock absorber, just like the shocks on your car. The only way a bolt will have "less" recoil is if the bolt gun is significanly heavier than the semi (same energy trying to move more mass equals less force transferred as fast to the shoulder).
For extreme examples of this, look at artillary pieces. Unless they are in a massive fixed mount, almost ALL arty pieces have some sort of recoil damper system, as all of them are mechanically similar to a bolt gun (breach stays closed till they manually extract the shell).
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