Well, I'm learning something new here I guess.
Still not sure why the need for rifling though.
The original Lemat was not rifled and Pietta makes a copy of it. I do not know if the repro is rifled.
FWIW...
http://en.wikipedia.org/wiki/LeMat_Revolver The rifling makes it a rifle. Not my logic, BATF. The H&R that Dave posted is a good example. People have been trying for years to get BATF to allow them, no dice. I gave up the thought of buying one, once I spoke to BATF and they explained the necessary paperwork.
If you are in possession of the receiver and the barrel, you are potentially in violation of the law, unless the gun was originally registered and you are in possession of the tax stamp.
As for the LeMat, I have no idea what their logic was / is.
Pete