Since there's through confusion right now, I'm going to ask my own. Is the barrel length on a form 1 the only length that SBR can have or is it freely changeable? Like if I put 12.5" on the form but want to change to 8" down the road, is that allowed or are there more forms? Also, changing chambering. Like from 5.56 on the form to 6.5 grendel later.I'm an 07/02 SOT with 30 years experience. You don't know where to engrave a caliber marking. We are not the same