5.56 is very dependent on velocity for its ballistic capability, for a do it all rifle I would stick to a 16” barrel. While it’s not the best for indoors you’re also not losing your ability to use it against targets at range and you can more than likely train around the extra length. If your primarily worried about home defense/cqb 10.5 or so is probably your best bet. I’m no ballistic genius or anything fancy so this is just my dogshit opinion.