In this context, muzzleloaders and black powder guns usually refer to antique or “curio” firearms. These types of weapons are in a special category under Texas and federal law because the legal definitions of “firearm” specifically exclude certain antique firearms.
Texas law makes the following exemption from the definition of “firearm” in Section 46.01(3) of the Texas Penal Code:
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.
Federal law defines “antique firearm” in a very similar way at 18 U.S. Code 921(a)(16). Much like Texas law, “antique firearms” are not included in the legal definition of “firearm” (see 18 U.S. Code 921(a)(3)).
These exemptions are important because both Texas law and federal law restrict people who have been convicted of certain offenses from possessing firearms — a legal term that does not include many antique weapons like muzzleloaders.
The Federal Bureau of Alcohol, Tobacco, Firearms, and Explosives has an FAQ regarding whether a “prohibited person” can possess a black powder or muzzle loaded weapon:
The Gun Control Act of 1968 (GCA) prohibits felons and certain other persons from possessing or receiving firearms and ammunition (“prohibited persons”). […] However, Federal law does not prohibit these persons from possessing or receiving an antique firearm.
For more information on antique firearms, please see the ATF's definition of “antique firearm”, along with some illustrated examples. The library also has more information on firearm restrictions for convicted felons on the Felons & Firearms page of our Gun Laws research guide.