Clarify please

[wnchstrtnfldvlle]

I have a lower that can be made into either a pistol or a rifle, and a lower that came on a sig m400. My idea is to use the factory assembled lower for the ar15 pistol I am going to assemble, and the other lower for the rifle. Legal? I know they can go either rifle to pistol, or pistol to rifle. Just not sure which one.

Reason is the rifle just gets shot occasionally, so I wouldn't be nervous using a lower that I put together, and will shoot the crap out of the pistol lower, so more comfortable using a factory assembled lower.

Or does it really matter?

 

[jlcnuke]

The lower that came with your rifle cannot be used to make the pistol, without following the appropriate class III requirements and getting ATF approval and paying the $200 tax stamp.

See classifications here http://www.atf.gov/firearms/guides/identification-of-nfa-firearms.html#made-from-rifle

Ruling here http://www.atf.gov/regulations-rulings/rulings/atf-rulings/atf-ruling-2011-4.pdf for explanations of what constitutes "weapon made from a rifle" and "pistol".

 

[wnchstrtnfldvlle]

Thank you