According to federal law, BP revolver is not a Gun, so you have to check your particular state law. So...Texas..
Sec. 46.01. DEFINITIONS. In this chapter:
(3) "Firearm" means any device designed, made, or adapted to expel a projectile through a barrel by using the energy generated by an explosion or burning substance or any device readily convertible to that use. Firearm does not include a firearm that may have, as an integral part, a folding knife blade or other characteristics of weapons made illegal by this chapter and that is:
(A) an antique or curio firearm manufactured before 1899; or
(B) a replica of an antique or curio firearm manufactured before 1899, but only if the replica does not use rim fire or center fire ammunition.
Law enforcement cant enforce Disorderly Conduct laws againt it either. Althow you can get youself in trouble for other actions, but 42.01 disorderly conduct with the intent to calculate alarm isnt one of them if you are simply carrying the "Antique" on your person.
Sec. 42.01. DISORDERLY CONDUCT. (a) A person commits an offense if he intentionally or knowingly:
(8) displays a firearm or other deadly weapon in a public place in a manner calculated to alarm;
Black Power Antiques are not considered to be Weapons or Firearms. And Welcome to Texas.