Person very familiar with NFA items

[275RLTW]

No, an SBR is an SBR. You can put a barrel of any length on an SBR, longer or shorter than what's on the form 1. As you stated, if you permanently change the configuration as written on the form 1 (read: you sell the original parts and don't have other parts to assemble to the same dimensions/caliber) you submit paperwork to amend the form 1.

Incorrect. You cannot go shorter than what you have listed on the Form 1. ou would have to request permission to modify the original Form 1. You can always go longer, but not shorter. And an SBR lower created on a Form 1 can be made back into a "regular" lower (non NFA) again if you so wished.

And a correction to my earlier post:

You cannot purchase the short upper(s) until a Form 1 has been sent in and the firearm registered. http://www.atf.gov/firearms/faq/nati...art-possession