Actually Holden, you are incorrect in your assumption that an ex-felon cannot own a black powder weapon or the propellant for it.
Title 18 USC, Section 921 (a)(3) establishes the definition of a "firearm" as follows:
"(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."
Title 18 USC, Section 921 (a)(16) further defines an "antique firearm" as follows:
"(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."
Now, let me address Texas law. The legal definition of a "firearm" in Texas statutes is provided by Title 10, Section 46.01 (3) of the Texas Penal Code, as shown below:
"(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."
Granted, this definition is not as broad and straight-forward as the Federal definition, but it clearly appears to encompass black powder weapons.
Additionally, if you would care to check the container packaging of all commercial black powder (and black powder substitutes such as Triple 7 and Pyrodex), you will find a statement that these propellants are not legally classified as explosives. Therefore, they are legal for anyone to possess and use for any legal purpose.
In short, an ex-felon has an absolute right to own, use and possess any black powder muzzleloading weapon under Federal law; this may be open for interpretation in the State of Texas, but I believe that it is legal under Texas statute also.