Does that mean I can't put a different upper on it or what?

I was under the impression that if your lower is engraved "multi" caliber from the manufacture, you were good as long as your barrel is engraved with the caliber. I could be wrong though.

MULTI is completely meaningless, as far as legally required engraving goes.

I would send it off and have it engraved.

I won a free NFA engraving from molonlabe.com a few years back and they did an excellent job.

They get all of my future business for supporting this site and the great job they did.

As far as upper, you can swap out as many different uppers as you want. It's generally recommended to keep an upper with the size barrel you registered (so if you put 10.5" barrel always have a 10.5" barrel laying around). If you decide to permanently go shorter you just need to notify the atf.

I built one of mine as a 223 and decided to build a 300blkout. I sent them a letter than they sent be a letter back that the permanent change had been noted.

PS. I am not affiliated in any way with the company.

That is not a requirement. It's just recommended.

I see

I think

Since they started tbe online thing, is there anyway for me to check the status of forms i mailed in?

Not online. Just by calling.

another option for your buffer tube is one of those condom type covers made for tennis racket handles. Thats what I used until mine was approved. was a few bucks from walmart.

Yes, I goofed there.  Sorry.