I'm playing around with the idea of building an SBR. This'd be my first so just checking my thought process before I move forward on anything.

So i'd be building it myself, so will order a stripped lower get it stamped then do form 1, waiting for that to be approved while i build it up.

once that gets approved I'd like a 300 blkout upper, but I'd also like to be able to switch it out with a 556 upper (on the same lower).  Can I legally do this on the same lower? or does anything (stamp, info on form 1)  prevent me from doing so?

thanks for the help

Once you have an approved Form 1, and you've built your rifle in the specified configuration, you may swap uppers at will, irrespective of caliber or barrel length.  ATF requests, but cannot legally require, that you inform them of any "permanent" configuration change.  What constitutes a "permanent" configuration change on an AR-type weapon is up to you.

Yes as long as you keep the original 300 upper

No problem with what you want to do.

Buy your lower, decide if you want to do it as a trust or individual - have the lower engraved with your or your trusts info, city & state you plan on making the SBR in.

Send in your Form 1 to BATFE either by mail (individual) or via EForms if you go trust. On the F1 you must declare caliber, barrel length & overall length, and you should build it to those specs the first time once you get the approved tax stamp.

From that point on - you can buy/make as many uppers as you wish - change calibers, change barrel lengths, etc...  The BATFE "suggests" you inform them on any permanent changes, but it is not required (at this time, anyway).

I have a AR pistol with both a 5.56 & 300 BLK uppers - my F1 for a different lower has been submitted as a 10.5" 5.56, but will be using both on the SBR once its been approved. I also plan on a SBR 22LR upper...

Decide what you want, and get in the pool!

Take care,
Bob S.

I used to think that also - but I have found this not to be true. You are under no obligation to be able to return it to the original specs submitted on the F1.

The only time it would come up (as far as I can see) would be if you wanted to sell your SBR to someone, and the F4 info didn't match - the simple solution would be to inform the BATFE of a permanent change prior to the sale of the current configuration.

Take care,
Bob S.

A myth that needs to stop being spread.

Thanks everyone.  now its time to stop chatting and start shuffling around finances :-)

Agree. I can't find any legal basis for this rumor.