Since the ATF rules all 50bmg AR uppers now as a actual firearm what part of such setup would need to be the stamped & serialized part?


The Upper?
The lower?
Both?

I'm thinking both.
Upper is a rifle (correct?) and so would need a stamp.
Lower now has a <16" barrel attached and so, too, would need an SBR stamp.

That's my thinking.

How short you going?
Any thought to having a brake P&W to bring you to 16"?

Im going for full blown range toy retarded lol.

I was thinking like 12" and having a custom brake made for it that would look similar to the ones on boys anti tank rifles.


When the trigger is pulled I want it to birth baby suns...

I think you'd only need to SBR the .50 BMG upper/firearm.

You can have a Master Key 870 (SBS) and attach it to a Title I AR and that's fine.

You're not making a second short-barreled firearm by doing that.

Sure the .50 requires a host lower to work properly, but it's still a firearm all by itself and therefore the logical component to register.

The upper is a "firearm"

I have the vague recollection of Safety Harbor having this conundrum when they built their 12.5" and just took the easy route by building it as a pistol

I hope this is the correct answer.

Paradox here is that the upper is not a “rifle” until it’s attached to a lower with a buttstock. And the lower with a buttstock isn’t a “rifle” until you attach a barreled upper.

My guess is this is a 2-stamp gun. Both “firearms” become “short-barreled rifles” when attached to each other.

Pull a T/C and file for both, then sue them to get your money back.

In all reality, it would likely just be one stamp, but then the completed assembly would be married.

If you want to divorce, you'd then have to file for a 2nd SBR for the lower similar to HK sears and host.

I agree with you there.

It's likely that if you already have a SBR AR (lower) you could just install the .50 upper on it...
OR register the .50 upper (since it's a Title I firearm by default) as a SBR and then install it on any lower.

No it wouldn't be.

It would just be one SBR.
Nothing is keeping it from going back to how it was previously.

That isn't exactly how it works...

If you have a registered legacy HK conversion device (sear or pack/housing) then you can remove it from the host at any time, and use it in any host that it fits in (or was designed for, I should say, per ATF).

The host just can't be reassembled with a stock and a short barrel at the same time. It can stay disassembled, or (if it didn't start out as a rifle) you could reassemble it as a Title I pistol while the MG is elsewhere (like in another host).

The "married" HK conversion devices were typically improper registrations to begin with, and some can be "divorced" by registering the original host as a SBR, but others are stuck together forever. It just depends on how wrongly the conversion/registration was done. That's usually what people are referring to when they discuss "divorcing" an HK sear, but sometimes they are simply referring to registering a host as a SBR so it can retain the short barrel and stock without the MG present.

Well I have a few sbr lowers I was kinda thinking this would be its own stand alone sbr.

Hence the single shot lower in the op.


When a 50bmg upper is sold does it transfer as a rifle or receiver?

Should be Other (firearm).

(This is assuming it's been classified as a Title I firearm by BATFE.) That's all of them now, right?

Although one guy above said a certain company designated theirs as a Handgun.

Yeah, after thinking more about it, that's how it would have to work since removing the upper removes the short barrel.

Since the short barrel isn't attached to the lower it no longer falls under the SBR classification, just like selling a stripped SBR receiver as a title 1 firearm.

The HK "divorce" I was referring to was where a registered conversion device was installed in something like a HK94 with the barrel chopped down, and registering the HK94 as a SBR frees the conversion device.

Not exactly the same situation though since the short barrel remains on the HK94.

Exactly.

If that's incorrect then ATF would have to explain why.

I fail to see how one short barrel and one stock could ever equal possession of more than one SBR, even if there are 2 (or more) receivers involved.

Right, but with the stock removed, the HK94 isn't a SBR either so the conversion device is still free to go wherever.

I understand some people still desire to reassemble their HK hosts as semi-auto SBRs, but I just swap the registered MG pack around to a bunch of unregistered host firearms (since the stock has to be removed anyway to take the pack out).

I don't really like shooting any of the short ones in semi-auto anyway, and they're easier to sell as Title I pistols (if I ever decide to sell any).

If I were you I’d...

A) Buy the upper. Have your name/city/state engraved on the barrel.

B) Buy an 80% lower engraved with your name, city, state, caliber, model name and serial.  Make sure the “model” and “serial” on the 80% receiver are identical to the upper’s model and serial.  

C) Submit a Form 1 that describes:
AR15 SBR as the type of weapon
Write down the measured OAL
For caliber, just put  “.50“
Your name/city/state as the maker
Then list the Model name & Serial

D) finish the 80% lower and send it out for proper finishing if it wasn’t already anodized. Keep the upper and lower exclusively paired together.

You should be fine. There’s no conflicting info written on the upper, lower, or form 1 ... and so long as you keep that upper exclusively for use with that lower, you never have more than 1 SBR.

It would be smart to get some ATF guidance on this before just heading out. In the end, you do have two separate firearms that combine into a single SBR in this case, each predicated on the other. While there are a lot of multiple-firearm situations under the NFA, some single stamp, some double stamp, as discussed, there are none quite like this.

I’m also certain that this is not the first time this has come up, so I’m sure there is a specific NFA pathway already established for this.

OP, I think you’re overthinking this... If you want a 12”-ish inch barrel and a crazy brake, just pin-weld an Armalite AR50A1 brake to a 12.5” barrel.

I’m measuring mine and it adds 3.740” to the barrel. That would be almost 16-1/4” if pinned to a 12.5” barrel.

And there’s no denying the Armalite brake looks awesome and throws yuge fireballs on barrels. I’ll bet it’d take your eyebrows off if you did a M99-style bullpup with pinned Armalite brake.

Attached File

Was the whole deal with the uppers ever clarified? Last I had heard it was only safety harbor that had received a letter.  So dumb.

So like... not to advise playing with fire but... What's to stop you from cutting down the barrel and putting the upper on a pistol lower? Just because both upper and lower are "firearms" and there is no stock, would this not be a possibility? I mean, the atf probably wouldn't see if that way if you asked them but for the hypothetical I'm not seeing why this wouldn't work.

tagged for future reference.

Only one way to find out

I might try to shoot one without it shouldered but I certainly wouldn’t want my face anywhere near the back of it

Attached File

That maybe the best way.

I have no idea actually how short it will be without getting my hand on the upper.

If you see the one I have linked it appears to have a rail/handguard that actually makes contact with the barrel in 2 places. So would be right in front of that.

Also how bad is that brake at throwing gas back at the shooter?

A pistol chambered in .50 BMG is actually a
Destructive Device. Rifle bores are measured by the lands, pistols by the grooves, so a pistol in .50 BMG is actually a .51 bore diameter.

This is why you don’t see these very often. That and the fact they are painful.