Kingcreek might be right on that. I had an old Remington Model 11(Same as A-5) and it kicked like h*ll when set up wrong.
Also, felt recoil is a function of weight. The Sweet 16 is on a smaller frame than the 12.Bet it runs not much more than 6 lbs.
Daughter's 20 ga 870 Express Youth is a very light little gun, and recoil is,well, stiff.
May have to get a solid brass mag plug made for practice.