So, I have an SBR issued to me by my agency. I love it! Now I want my own. I have another AR and was wandering, can i buy a new upper for my lower and go that route? I know i gotta do the paperwork, but was thinking if i could just swap uppers, i could sell one of my carbine length uppers and get a SBR upper. I hope I'm explaining myself so yall know what I'm thinking. Thanks.