Changing Your SBR Upper with a Different Caliber Than the Registered Lower Generator

Changing your SBR upper with a different caliber than the registered lower is possible.  Since you can't use "multi" caliber on the ATF Form 1 application anymore, many people ask us.  Can I change the upper caliber on my registered [tax stamped] lower SBR?  The answer is yes. There a few ways to do this.  The ways we recommend to do this with our clients are below:

Add this information on your ATF Form 1 (5320.1) application:  To do this you can use box 4h. Additional Description.  Your gun trust information normally goes here, if you are registering the SBR with a NFA Gun Trust.  But you can also add additional calibers and barrel length configurations here.  The ATF recommends to use this space for that because they only want one caliber and one OAL in the boxes 4e and 4f.  If you have further questions about how to fill out your ATF Form 1 (5320.1 -ATF 5320.1 Application to Make and Register a Firearm), you can check out our ATF Form 1 walk-through guide here. 

Send a letter to the ATF with the new calibers and/or barrel lengths:  If you already have an approved tax stamp from the ATF then you can simply send a letter to the ATF describing which uppers you are planning to use with the your SBR.  When you send a letter to the ATF, send the letter in duplicate and request a letter back from the ATF confirming that received/approved the letter.  What you need to include in the letter is the make, model and serial number of your lower, who it is registered to, the caliber and OAL (overall length) of the new uppers that you want to add to the SBR.  Below is a Changing Your SBR Upper with a Different Caliber Than the Registered Lower Generator that you can use with the ATF to notify them of these additions.