Ditto. I would purchase a small amount of .600 and .610 balls and see which work best with a .018 pillow ticking patch.20 gauge is a .62 caliber. I used to own a .62 caliber smoothbore and loaded a 20 gauge shotcup and then bird shot and then an over the shot card. When I shot roundball out of it I shot .600 or .610 when I could find them. Accuracy was good to 40 steps. With a pistol I would get real close. Other then that I am not sure what yours would take. There must be a manual with it you would think.
Only if you want a really pissed-off intruder. A fellow once sent me an old original English .54 smoothbore pistol to jug choke for shot. I tested it at 15 yards by firing on an old Goex powder can. Hit it with 8 or 10 number 6 nickle plated shot but not one pellet penetrated the front side of the can. I often use those steel Goex cans to test penetration of birdshot loads and I'd not hunt small game with a load that won't penetrate both sides.I agree, Pete. I think the Howdah pistol loaded with #6 or #4 shot would make a great home defense weapon, if you didn't burn your house down from that muzzle blast!