How Do I Change the Registered Configuration of My Short-Barreled Rifle?

You have filed an ATF Form 1 application make an existing firearm into a short-barreled rifle (SBR). The ATF finally approves your Form 1 application and mails the approval document (the “tax stamp”) to you. Your tax stamp allows you to convert your firearm to the specific configuration of barrel length, overall length, and caliber that you requested, which you then build. Later, you decide to change one of more of the variables of barrel length, overall length, or caliber. What do you do?

For example, let’s say your existing SBR has a barrel length of 10.5 inches, an overall length of 29 inches, and a caliber of 5.56 mm. You would like to change out the upper receiver to convert it to 300 AAC Blackout with a 9 inch barrel. In addition, you want to be able to use a 7.5 inch, 5.56 mm barrel in the future.

You can lawfully amend your tax stamp to include multiple configurations.  Simply send a letter to the ATF stating the details of each additional configuration, including barrel length, overall length, and caliber.

Important Note: Do not request the ATF to replace the existing configuration with a new configuration. Instead, request the ATF to amend your existing registration to include a new additional configuration.

Next Important Note: Caliber refers to the diameter of the bullet only, not the length, so do not add information relating to the length of the bullet, such as .22 LR, .45 ACP, 5.56 x 45, or 300 AAC BLACKOUT. Some ATF examiners will reject applications that include information relating to bullet length.

For example, a letter requesting additional configurations for an SBR owned by your gun trust would look something like this:

Ima Gun Owner, Trustee
My Gun Trust
123 Main St.
Austin, TX 78701

April 10, 2017

National Firearms Act Branch
Bureau of Alcohol, Tobacco, Firearms, and Explosives
244 Needy Rd., Ste. 1250
Martinsburg, WV 25405

Dear Sir/Madam:

Please amend the previously approved attached Form 1 with the following additional configurations:

Barrel Length

Overall Length
Caliber Unit of Measure
9 27.5 .300 caliber
7.5 27 5.56 mm

If you have any questions or comments, please do not hesitate to contact me by telephone at 512-288-3200.  Thank you for your assistance in this matter.


Ima Gun Owner, Trustee
My Gun Trust


You may or may not hear back from the ATF. Just keep a copy of the letter that you sent in your file so that, if challenged, you can show that you notified the ATF of the additional configurations.

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