The advantage of pump is low price plus reliability. The twelve gauge allows user to select very fine "tactical" (lower velocity/lower recoil) loads. Both slug and buck shot are readily from several manufacturers. Those are not available in 20 ga and may not work in semi-auto firearms. For HD the 12ga pump gun is the obvious choice. In Canada wonderful affordable and low maintenance model is Hasan "Marine" pump action shotgun. In USA it's available under Dickinson name.
