it will depend on Bullet design a bullet that expands reliably at supersonic speed may not expand at sub sonic speeds and a bullet that expands reliably at subsonic speeds would most likely fragment (instead of expanding) at supersonic speeds as long as they will reliably function the saint, for home defense I would most likely go with the Hornady subsonic rounds hornady.com/ammunition/subsonic#!/

Supersonic will expand the most with regular bullets. There are bullet types designed to expand at lower Subsonic velocities that would be the best to limit over penetration in a self defense scenario. Hornady makes a very good loading specific for this purpose : hornady.com/ammunition/subsonic#!/

You will need velocity for expansion so I would go with super sonic. Something like Barnes tax-x. It’s solid copper with a black polymer tip.