On edit: Is there a difference in self defense laws regarding what type of weapon one uses? I haven't heard of one.
a. That Class III weapons are legal in the state.
b. The weapon used was properly registered and up to date.
c. The shooting itself, without regard to the weapon used, is justifiable.
Then there should be no difference what weapon was used. If you're talking a good self-defense shooting, based on the circumstances then the type of weapon used is moot. Most laws permit the use of "deadly force" or "lethal force", whether you applied it by hand, a 2x4, shovel, shotgun, or a 30mm Gatling gun.
Where you might
get into trouble is if it appears you excessively shot someone who might otherwise survived. Such as an intruder who doesn't drop his gun when told, but raises it -- and you let off a magazine of 5.56mm into him just as he raises his hands over his head. He may have survived a single gunshot wound, but not 10, 15 or 20.