Eugene Volokh takes a look at a decision in California State Court of Appeals that rules .50 calibers are not constitutionally protected. I think the state court’s analysis of the commonality of these types of arms is deeply flawed, as they are indeed “common” and not any more “dangerous” than other firearms that the State of California has not seen fit to ban.
I also don’t think one can take a self-defense approach to the Second Amendment that only considers self-defense under average circumstances. A Barret M82, or an AR-15 may, under a state of civil order, not be ideal firearms for self-defense under most circumstances. But what about a state of civil disorder? I don’t think self-defense under extreme circumstances can be so easily dismissed.
As I’ve argued, like Professor Nelson Lund has also, that any analysis done under Heller’s common use test has to also consider police use. Does a .50BMG pass this test? I think it would be hard to argue they are common in police arsenals, though some exist. But I would also argue that it is not especially dangerous, compared to other small arms.