Interesting Topic for This Forum
I remember two articles concerning this very topic. In one article, they shot a mock sheetrock wall with various sizes of shot with an 870 riot shotgun and found the maximum size to safely use(for neighbors, children in the next room) was #6 birdshot. In another article(by Chuck Taylor, one of the leading .45 experts in the world), recommended 7 1/2 or #8 birdshot used with a coachgun-style shotgun(seen in almost any John Wayne that had a stagecoach scene). Much safer, easy to use by anyone, less muzzle velocity than your hunting shotgun...