TexasCHLforum.com

Here's one caution about "antiques" (made before January 1, 1899): while they might not legally be firearms, the ammunition can get you in trouble.

I'll have to search for it later, but I read about a case in the past couple of years, where a felon deliberately owned a pre-'99 revolver to avoid that charge. There was an accusation that he'd shot at someone, his car was searched, the gun was found, and he was convicted. Not for being a felon in possession of a firearm, because he raised the "antique" defense, but for five counts of being a felon in possession of "ammunition or ammunition components" for the (IIRC) three empty shells and two live rounds in the revolver.

That doesn't apply to cap & ball arms, but there are lots of antique firearms that fire modern ammunition. That ammo is a no-no for felons.