According to the folks I contacted, as long as the firearm is set up according to factory specifications, they are legal to set up either as a handgun or a rifle/carbine. T/C has NO DOCUMENTATION that explains how to install a handgun barrel with a carbine or rifle stock set up. The T/C literature is very clear and is specific for handgun and rifle to include stock/grip description and barrel lengths.
http://www.tcarms.com/manuals/12Ga Muzzleloader Supplement | Adobe .PDF (579 KB)
45 Super Load Charts | Adobe .PDF (123 KB)
Black Diamond Manual | Adobe .PDF (1608 KB)
Encore Muzzleloader Manual | Adobe .PDF (2219 KB)
Encore Pistol Manual | Adobe .PDF (646 KB)
Encore Rifle Manual | Adobe .PDF (6293 KB)
FireStormManual CL and FL | Adobe .PDF (3944 KB)
G2 Contender Manual | Adobe .PDF (671 KB)
G2 Contender ML Manual | Adobe .PDF (1341 KB)
Icon Manual | Adobe .PDF (2572 KB)
Omega Muzzleloader Manual | Adobe .PDF (1393 KB)
R55 SemiAuto Manual | Adobe .PDF (632 KB)
Shooting TC Side Lock Black Powder Guns | Adobe .PDF (1791 KB)
TC Triumph Manual | Adobe .PDF (3263 KB)
Steve