Help with my proposed 2-stamp build

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My next project is going to be an SBR 9mm AR with a suppressor. I want to send off for my stamps ASAP but I need some advice first.

I have a half dozen or so 5.56 lowers around the house and could use one of them with a mag block, but am I better off buying a 9mm lower for the build since it's already marked 9mm? Does it matter?

How would I register a 5.56 lower for a 9mm build if I decide to go that route? Do you just register it as multi-caliber?

Thanks in advance for any advice.
 
You can ignore the caliber markings on the lower, they are irrelevant. It's not advisable to put "multi" as a caliber on Form1, apparently it can get rejected for that reason. You can list several calibers on form1 or list just one and use several uppers with different calibers/barrel lengths with your SBR lower, it's totally legal as long as you can return your SBR to the configuration listed on Form1.
 
You can ignore the caliber markings on the lower, they are irrelevant. It's not advisable to put "multi" as a caliber on Form1, apparently it can get rejected for that reason. You can list several calibers on form1 or list just one and use several uppers with different calibers/barrel lengths with your SBR lower, it's totally legal as long as you can return your SBR to the configuration listed on Form1.

Thanks, that was what I was looking for.

For some reason I had it in my head that a registered "9mm SBR" could only be configured as a 9mm.

I'll use one of my 5.56 lowers in that case.
 
when you file the form 1, you become the "manufacturer" which is why you need to engrave your name/trust/LLC name on it. submit it as 9mm on the form 1, after that you can change the caliber as much as you want--the ATF says it's polite to tell them if you do, but there's no legal requirement to do so.
 
+1 on the caliber marking not mattering.

I went with a CMMG dedicated 9mm lower for my 2-stamp 9mm AR build. I got the barrel from ADCO. I want to say it's a 7.5"? I got my 3 lug adapter from TROS. With the 7" MI T7 FF rail, only the adapter is showing. I didn't want to have the rail longer than the barrel since I don't always shoot it suppressed.

A friend of mine did one with a DDLES lower, but I don't think they're a company anymore. They had all sorts of issues with not delivering products, stuff not working, etc.. Research them if you decide you want a DDLES lower. He waited months for his, and IIRC had to send it back to have something machined because it was out of spec. It's a neat concept to use Glock mags, but IMO they're ugly lowers, and the Colt 9mm SMG mags are easy enough to find and not TOO expensive.

I use a CMMG ramped bolt in mine, Spikes ST-9X buffer, and a regular LPK/buffer spring.
 
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OK, changed my mind and decided to go with a dedicated 9mm lower. Any suggestions on mfg?

Also have a question on which comes first: the engraving or the Form 1.

Thanks.
 
Also have a question on which comes first: the engraving or the Form 1.

Thanks.
You can do it either way. You can get stuck with engraved lower in case your Form 1 is rejected (and still use it for non-NFA build) or totally unusable Form 1 in case your lower is lost/damaged or the engraving is f..d up. i
 
There's a guy that can engrave your lower while you watch, in Nashua. I've used him for every SBR I have. PM me for his contact info, IDK how the advertising rules work. Send your form 1 the second you pick the lower up to get it rolling, cuz thats the long lead item.

I still say CMMG for 9mm lowers. Not sure who else makes them. I think LWD does now, and they use Glock mags?
 
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