[dogtown tom]

SDC:...But the lower of an AR pistol bears a serial number that can be definitely be PROVEN to have been a rifle OR a pistol when it left the factory...

Nope. Not in all cases.

Stripped or partially assembled AR lowers as well as other firearm frames and receivers are not long guns or handguns- they are considered an "Other Firearm" in the eyes of the ATF. Lowers, frames or receivers are not considered long guns until they have had a shoulder stock attached.

I've never had a manufacturer ship me an AR lower and tell me it was a rifle lower or pistol lower.

gyvel: OK. Playing devil's advocate here, where would the burden of proof lie if you had a bare receiver and insisted that it had never been a "rifle." ATF would have a hard time proving otherwise, no?

If you can show where and how you obtained a virgin receiver you'll have no problem. In a criminal trial ATF would have the burden of proof. While you might prevail, you would undoubtably run up legal fees far in excess of that $200 tax stamp.