TexasCHLforum.com

I think above addressed Federal Regs, but add Texas Penal code

10) "Short-barrel firearm" means a rifle with a barrel length of less than 16 inches or a shotgun with a barrel length of less than 18 inches, or any weapon made from a shotgun or rifle if, as altered, it has an overall length of less than 26 inches.

What I did in the 1970s was cut the barrel 18.25 inches (measured inside barrel), then measure how much stock to cut to stay over 26 inches overall