The AO T1B with detachable buttstock is ok, the overall length is 31.5 inches with the butt removed.
“a weapon made from a rifle if such weapon as modified has an overall length of less than 26 inches or barrel or barrels of less than 16 inches in length”
Think about it this way. Add a vertical grip to your AR15 carbine quad rail, then take your 6 position stock and slide it off the buffer tube. Did you make it into a SBR or AOW?
THE ATF NEVER INCLUDED THE THOMPSON PISTOL
WITH A FRONT GRIP AN AOW THIS WAS ONE THE EXCEPTIONS TO THE RULE.
AUTO ORDNANCE (THOMPSON) MADE THE PISTOL FOR YEARS AND IT COULD BOUGHT RIGHT OVER THE COUNTER…
As I understand it, any recognized long gun would only require the $200 stamp if the OAL, with or without a stock was less than 26-inches (I think) OR the barrel is less than 16-inches.
A handgun, on the other hand, requires the tax if you either add a vertical foregrip or a stock without dropping in a 16-inch barrel and meeting the minimum OAL of 16-inches.