I haven't filed for an SBR in while but If I recall, you could purchase an AR lower and just submit it as "Multi Caliber" and then just put whatever caliber or barrel length you wanted... which made things simple. Now you can't do this???? each SBR requires a specified caliber and barrel length? I have read that you can request a change or addition to your lower but you have to request from the ATF, which is something I'm trying to avoid. Anyone know a better way to have just one AR Lower as an SBR and then add whatever upper you want?