Gramp's old 12-ga shotgun with 3" shells, particularly if it was not too heavy, has recoil similar to a .416 Rigby with 400-grain bullets. The .300 magnums of various designs only produce about half as much. However, you will FEEL more pain when shooting arifle from a bench while zeroing and testing ammunition than you will notice when shooting a shotgun at game in the field. But when you shoot your .300 at an elk or moose, I guarantee you won't feel any recoil at all..... (IF you can shoot that old shotgun with slugs at a paper target from a benchrest, you will have NO TROUBLE at all with one of the .300 Magnums!)