SBR Lower Question

[Lamented]

If I purchase a complete SBR rifle. Am I able to purchase multiple SBR uppers for that particular lower? Or is it one upper per registered lower?

[ggammell]

One lower with all the uppers you could possibly want.

[NickB]

What about switching calibers and/or barrel length after my Form 1 stamp is approved?
Your Form 1 was approved for a specific caliber, overall length, and barrel length. However you are allowed to “temporarily” change the upper length or caliber but only if you maintain the original upper and ability switch back afterward. If you sell the upper and switch permanently to a different upper then you would need to send a notification to the ATF letting them know of the official change. You don’t pay the stamp or go through the Form 1 process again, just a notification.

Link: https://www.rainierarms.com/blog/atf-form-1-creating-or-manufacturing-your-own-sbr-faq/

[BigWaylon]

There's still no "need" with a permanent change. They recommend you do it, but can't require you to do it. There are even examiners that will tell you they don't ever want to see another change letter for an AR-based SBR because nothing is permanent. Even if you sold the up you could have a replacement in a couple days.