Multiple uppers for SBR lower

[Madranchtx]

I'm waiting for the tax stamp on a factory SBR in 5.56. Once it is my possession can I purchase a short barrel 300 blackout upper and use the 5.56 lower?
My understanding is it is OK to use a different upper of the same caliber, I'm not sure if you can use a different caliber. I don't see why not but I don't work for the government either.

[BigWaylon]

You can attach any upper you want to it. Doesn't matter if it's >16" or <16", or what caliber it is.

[JulyAZ]

Once you SBR your lower, caliber, and barrel length and pretty much a non issue.

Have fun, some people do call the ATF if you make a permanent change but for the most part the general consensus is don’t worry about it.

[markm]

You have to mail them notice every time you squeeze off a live round that's outside of your original form. To play is safe, I facetime my shoots directly to the ATF.

[Madranchtx]

Thanks guys.
markm-please quit, maybe the wait time wouldn't be so long if the ATF guys where processing forms instead of watching your facetime:)

[markm]

Good point. I'll just go black ops on my NFA activities.