Black power pistols are not "firearms".
They're "antique firearms" (even if they were manufactured this morning), an entirely different sort of creature. Under federal law, anyway. As such, they are not subject to any of the federal legal restrictions (FFL, NICS check, age limits on purchase, etc) which apply to "firearms".
Of course you are correct...........
That said, I'm sure we all wish the Sandy Hook principal had been able to rush the mad gunner with a loaded Colt's Baby Dragoon instead of just her bare hands. She'd be alive today, and that SOB would still be dead, but without taking all those little kids and teachers with him, the sorry b@stard.