Sig 556 SBR and Swapping Lowers

[ShakyJ]

I purchased a Sig 556 pistol a few years ago and registered it via ATF Form 1 as a SBR. I have gotten a little bored with the current set-up and am thinking about swapping the current Sig 556 lower for a Sig 551 lower (probably the new 551-A1 as the original swiss lower is a little too pricey for me). Anyway, since the upper is the registered part, I assume there is nothing wrong with swapping to a different lower? The only thing I can think of that might cause a problem is that the new lower would have the Swiss folding stock, whereas my current set-up has a Magpul UBR (overall length will probably change). Otherwise, the barrel length and caliber will stay the same. I don't plan on getting rid of the original lower. So, do I need to submit anything to ATF? Or, since I'm keeping the original lower is it good enough that I can convert it back into its original configuration? Thanks for any help you all can provide.

 

[kimberkid]

As long as the length stays the same ... or you retain the parts so it can be changed back you are good to go.

I did the form 1 thing only I used a ACE M4 hinge interface set-up to make it a folder ... then earlier this year I bought a classic lower and Swiss stock for the SBR and put that original lower on another 556 that had the early receiver on it ... and sold the fixed receiver one for nearly what I paid for the classic

Back to the point ... the classic with the Swiss stock is a bit shorter overall length so I called our friends at the BTAFE and was told that as long as I could switch it back there was nothing I needed to do.

 

[RAINS]

Funny my factory 556 sbr has that sig adjustable stock. I wonder how they rate the overall length?
Put that Swiss style stock on you 556. Putting an AR stock on them just looks wrong somehow.

 

[MasterSergeantA]

You can put any lower you like on your Sig. The upper is the part that determines the gun's status. The only issue with the stock is if your local area doesn't allow "folding" stocks as compared to extendable ones. If there is a significant change in the OAL (with the stock fully extended...the way ATF measures things), you might consider dropping the ATF a note explaining the change. I enclose a copy of the original Form 1/4 with correspondence like that and always keep a copy in the files.

 

[FIVETWOSEVEN]

Would you buy a 551 and just switch lowers? How come the upper is the "gun" anyway?

 

[MasterSergeantA]

Sig has made the upper the serialized (the gun) part.

 

[Ar180shooter]

Would you buy a 551 and just switch lowers? How come the upper is the "gun" anyway?

For the Sig 55X series of rifles (American and Swiss made), the upper is the serialized part that is registered.

OP, from my understanding of American Law, you should be OK to switch the lower, especially since the rifle is already registered as an SBR.

 

[JustinJ]

I think that if by doing so it does not make any of the information on the ATF Form 1 untrue you should be fine so long as it does not cause any 922r violation which i don't believe it would. I don't recall though if all parts are US made.

 

[kimberkid]

I think that if by doing so it does not make any of the information on the ATF Form 1 untrue you should be fine so long as it does not cause any 922r violation which i don't believe it would. I don't recall though if all parts are US made.

According to my FFL/SOT and a ATF agent he asked that came to his shop on an records check ... NFA is NFA and by its definition an NFA item is not a sporting rifle, therefore 922r does not apply.

 

[TexasRifleman]

NFA is NFA and by its definition an NFA item is not a sporting rifle, therefore 922r does not apply.

That has always been my understanding as well. 922r is only for Title 1 firearms I believe. Once it has a tax stamp it's not a Title 1 firearm anymore.

 

[JustinJ]

Quote:
Originally Posted by JustinJ
I think that if by doing so it does not make any of the information on the ATF Form 1 untrue you should be fine so long as it does not cause any 922r violation which i don't believe it would. I don't recall though if all parts are US made.

According to my FFL/SOT and a ATF agent he asked that came to his shop on an records check ... NFA is NFA and by its definition an NFA item is not a sporting rifle, therefore 922r does not apply.

The most recent ATF letter on the subject clearly states that NFA items are not exempt from 922r. A link to it and the prior letter can be found here: http://gunwiki.net/Gunwiki/LegalFederal922rParts