I have an SBR question. Currently I own four AR15s in different calibers and barrel lengths (16-20). If I were to purchase a Multi Caliber AR15 lower receiver and then properly register it as a SBR lower, would I be legally allowed to own different caliber SBR uppers at the same time? I am guessing the answer would be no but since I did not see anybody ask about legally registering a Multi Caliber SBR lower, I thought I would ask. Thank you for your help.