Here is my original email to them:
Subject: Regulations concerning Short Barreled Rifles
In January of 2016, I submitted a Form 1 online to register a Short Barreled Rifle to my trust. The form was approved on April 27, 2016. The serial number in question is XXXXXXXXX. The description is for a 10.5” barreled AR15 rifle chambered in .300 Blackout. I realize that it is perfectly legal for me to mount a 16” or longer barreled upper receiver on this registered lower receiver, as barrel lengths longer than 16” are not limited by the NFA (even though the lower receiver itself remains registered as an NFA item). However, I have a question that I can’t seem to find the answer for anywhere, and I don’t want to jeopardize the legality of my current NFA registration.
Is it permissible for me to build a second short barreled upper receiver chambered in a different caliber (say, .223 Remington, or .458 SOCOM) to be used with that previously registered lower receiver, so long as the barrel length remains 10.5” or longer, and the overall dimensions with the stock extended is no shorter than the registered length provided for on my Form 1? In other words, would it be permissible for me to build a 10.5” barreled upper in 5.56x45mm NATO for example, and mount it on that registered lower, so long as none of the other registered dimensions change? The only change would be the diameter of the bore, and therefore the diameter of the bullet fired from that bore.
OR, would it be necessary for me to go through the entire registration process again, to reregister that lower receiver for a new caliber?
I hesitate to undertake such a thing without receiving guidance from you, as I want to stay on the right side of the NFA laws.
Thank you for any help you can give me with regard to this question.
The Annoyed Man
This morning, I received ATF’s reply:
Mr. Annoyed Man:
This is in reply to your recent email to the Firearms Industry Programs Branch (FIPB) Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) seeking information on your registered short barreled rifle (SBR). Specifically you wish to know if you may obtain additional barrels for this rifle in various lengths and calibers.
As way of background:
A "rifle" is defined as "a weapon designed or redesigned, made or remade, and intended to be fired from the shoulder and designed or redesigned and made or remade to use the energy of an explosive in a fixed metallic cartridge to fire only a single projectile through a rifled bore for each single pull of the trigger" (18 U.S.C. 921(a)(7).
The National Firearms Act (NFA) defines "short barreled rifle" as a rifle having one or more barrels less than sixteen inches in length (26 U.S.C. § 5845(a)(3)).
Also, the NFA defines “firearm,” in part, as—
“…a shotgun having a barrel or barrels of less than 18 inches in length….” (See 26 U.S.C.
Finally, the NFA defines “destructive device” in part as “any type of weapon by whatever name known which will, or which may be readily converted to, expel a projectile by the action of an explosive or other propellant, the barrel or barrels of which have a bore of more than one-half inch in diameter”…(see 26 U.S.C. 5845(f) )
Although the short barrels are the "prohibiting feature" within the definition which determines if a rifle is an SBR barrels themselves regardless of their lengths are simply firearms parts and thus their domestic possession and sale is unregulated.
Put another way, although the barrels are the prohibiting feature it is the rifle or more correctly the rifle receiver which is the registered item.
As you possess a registered SBR you may have as many barrels in whatever lengths and calibers you wish as long as that barrel does not cause the firearm to meet the definition of a "short barreled shotgun" or destructive device as each is defined above.
We suggest notifying our NFA Branch in writing of the additional barrel lengths and calibers so that they may modify the record of your registered SBR to reflect the additional lengths and calibers.
We thank you for your inquiry and trust that the foregoing has been responsive.
Michael S Knapp
Bureau of Alcohol, Tobacco, Firearms and Explosives
Firearms and Explosives Industry Division
First, I would like to say that the response only took 24 hours. When I had originally submitted the message, an autoresponder informed me that a response could take up to 90 days, so I was really pleased that it took just a day.
My original understanding was that I could probably get away with a second barreled upper, so long as the barrel length remained no shorter than 10.5”, since that determined the overall length of the weapon as originally registered. But the above paragraph in red seems to make it plain that the length doesn’t matter. I could have a barrel shorter than the original 10.5”, and that would not change the legal status of my SBR. The fact that the reply is signed by the Program Manager seems to lend weight to that assessment.