After doing my first NFA submission for a suppressor, I'm thinking about making an SBR now. When I looked at this years ago, you had to designate a caliber and other measurements. Is there a way to get an SBR approved so that I can put whatever upper (length and caliber) I want on it?

I want a 300BO upper, but then what if I want to put a 556 upper on it?

When you make an SBR, that’s a one-time act…and thus can only be a single caliber and length. But how you configure it after that moment in time makes no difference. Swap uppers to your heart’s content. And there’s no requirement for you to have to be able to return it to those original specs, regardless of what you may read online or here at a gun show/shop.

No requirement.  Now, the ATF is required to keep the registry as correct as possible, so you’ll see them recommend you notify them of certain things…but they can’t require it because there’s no statute/regulation to back it up.

The only time it potentially causes problems is if you file a Form 4 to sell it to somebody else, or file a 5320.20 to cross state lines, and it doesn’t match. I’ve changed barrel lengths (within the same caliber) and calibers (5.56 to 5.7) and never had an issue with a 5320.20. They did approved some “with conditions” when I filed one of them for .50 instead of 5.56. One examiner approved three with no note, and another put the condition on seven (all filed at the same time)…or vice versa. I argued with them that they had to statute to back up the “that’s too big a difference” excuse they gave me when I called and questioned it. Just another example of them making crap up.

@bigwaylon

Is your explanation about subsequent applications why people say you should keep the original upper?

Most people say it because they have no idea what they’re talking about.

Keeping the original upper might help for the F4 transfer, but how many people actually sell a registered Form 1 AR? You can sell the lower by itself with no NFA paperwork at all.

Keeping the original upper for a 5320.20 would be pointless if you wanted to travel with the alternate upper…unless you were taking two.