I thought I knew the answer to this question, but I have spent a good bit of time trying to locate where I originally found it on the ATF website in one of their FAQ documents with no success. I'm hoping someone can tell me where to find it again. My question is this: can a person remove the <16" upper of a short barreled AR, replace it with a >16" barreled upper and then transport the gun across state lines without having to fill out the ATF transportation request form? I've been told a whole bunch of times that a SBR is only a SBR when in SBR configuration, and that you can swap barrels back and forth all you want. I understand that, but can I go hunting in Ohio tomorrow with my SBS Remington 870 by putting a 28" barrel on it, or do I have to request permission first even when not in NFA configuration? More importantly, can someone please help me find verification of this on the ATF website or in the actual regs? Thanks in advance for any help.