So, Texas does not define a black powder pistol as a firearm if it does not use rimfire or centerfire ammunition and is a replica of one made on or before Dec. 31, 1898. This would make it legal for your friend or any felon to carry a black powder percussion revolver of the type that is a replica. They are commonly sold as kits to assemble, blue, and stain the wood yourself.(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.
. . .
(5) "Handgun" means any firearm that is designed, made, or adapted to be fired with one hand.
Please note that Texas law makes no distinction between a loaded or unloaded firearm, even in the case of black powder guns.
Federal law (18 USC 921) says:
So the federal law would also allow a felon or your friend to carry a percussion fired replica of a black powder revolver.(3) The term "firearm" means (A) any weapon (including a starter gun) which will or is designed to or may readily be converted to expel a projectile by the action of an explosive; (B) the frame or receiver of any such weapon; (C) any firearm muffler or firearm silencer; or (D) any destructive device. Such term does not include an antique firearm.
. . .
(16) The term "antique firearm" means -
(A) any firearm (including any firearm with a matchlock, flintlock, percussion cap, or similar type of ignition system)
manufactured in or before 1898; or
(B) any replica of any firearm described in subparagraph (A) if such replica -
(i) is not designed or redesigned for using rimfire or conventional centerfire fixed ammunition, or
(ii) uses rimfire or conventional centerfire fixed ammunition which is no longer manufactured in the United States and which is not readily available in the ordinary channels of commercial trade; or
(C) any muzzle loading rifle, muzzle loading shotgun, or muzzle loading pistol, which is designed to use black powder, or a black powder substitute, and which cannot use fixed ammunition. For purposes of this subparagraph, the term "antique firearm" shall not include any weapon which incorporates a firearm frame or
receiver, any firearm which is converted into a muzzle loading weapon, or any muzzle loading weapon which can be readily converted to fire fixed ammunition by replacing the barrel, bolt, breechblock, or any combination thereof.
(17)(A) The term "ammunition" means ammunition or cartridge cases, primers, bullets, or propellent powder designed for use in any firearm.
(B) The term "armor piercing ammunition" means -
(i) a projectile or projectile core which may be used in a handgun and which is constructed entirely (excluding the presence of traces of other substances) from one or a combination of tungsten alloys, steel, iron, brass, bronze, beryllium copper, or depleted uranium; or
(ii) a full jacketed projectile larger than .22 caliber designed and intended for use in a handgun and whose jacket has a weight of more than 25 percent of the total weight of the projectile.
(C) The term "armor piercing ammunition" does not include shotgun shot required by Federal or State environmental or game regulations for hunting purposes, a frangible projectile designed for target shooting, a projectile which the Attorney General finds is primarily intended to be used for sporting purposes, or any other
projectile or projectile core which the Attorney General finds is intended to be used for industrial purposes, including a charge used in an oil and gas well perforating device.
Please note the definition of ammunition, which I included because someone pointed out that felons could not possess it. Texas does not have that law, but it might impact your friend. If he carries real black powder or the replacement powder (not smokeless powder) that are not designed to be used in regular ammo, he should be okay. But since some modern rounds, such as the 30-30, were really designed for black powder and it may be claimed that they can still be made that way, he could get in trouble for carrying powder.