I'm thinking about Form 1'ing of my AR-15 lowers as a SBR and I have some questions.

1) Does the caliber listed on the Form-1 have to be the one marked originally on the receiver? i.e marked 5.56 but I want to make it a 9mm SBR

2) Would the ATF be likely to approve a listing like "9mm/.223/5.56mm" ?

I cant answer the first question, but I was asking the second one about my Form 1, and I was told that the ATF had been sending back some FOrm 1s marked with multiple calibers for some reason.