Joe is not to bright. An ar-15 shooting a hot load will be under 4 ft/lbs of recoil. A 20 gauge shooting a moderate load will be somewheres around 6-7 ft/lbs of recoil. A 12 gauge shooting an ounce and a quarter of OO buck will be around 30 ft/lbs. A 3" 12 gauge shooting a maximum load 1oz sabot at 1950 fps will be punishing.
Besides the fact that shotguns are very hard to handle in tight quarters because they are so long.