I've got a Colt 6920 that I've decided to SBR. I'm concerned about the model name I submit because it says M4 Carbine and not AR-15. Since I have to submit a pic of what's engraved on the receiver, and it doesn't say "AR-15" or "6920" do I put M4 Carbine where it asks for the model? Will that make the ATF freak out? I know I'm probably overthinking it but I'll be damned if I want my form to get kicked back by something so stupid.