I'm pretty sure every state, and the feds classify it as a firearm, but not a regulated firearm. So carrying it, all the same rules apply.
The Feds categorize them as "antique firearms," not as "firearms." Those two terms have specific legal differences as far as the Federal Government is concerned, the latter being federally regulated, the former not being federally regulated. According to them, in other words, an "antique firearm" is
not a "firearm."
That's my understanding on the matter, at any rate.
States are all over the place on their classification.