The only time the 12's become heavier recoiling rifles, is with the heavy BP loads of the late 1880's and 1890's. 151gr. 1F with a 480gr. or heavier ball or bullet will start to kick in an 8 pound, gun and 190grs. lifts the muzzles quite smartly.
: With smokeless loads duplicating these heavier BP ballistics, the recoil is very much lighter and no more than the old heavy duck loads with 1-1/2oz. lead shot - less recoil than about any 3" load.