Does anyone know of any significant issues with the ultra short SBRs on ARs? I'd like to build a 7" - 9" SBR in .223 just because I've had a fascination with a micro-CAR concept; an ultra compact, loud as hell, flame spitting SBR. I'm planning on using a Rock River pistol lenth upper in conjunction to a registered SBR lower that I will build. I'd like to have the ability to toss on a 16" upper for longer distance work and hunting. Another option is a 10.5" LMT. It'd save me from having to engrave it, and would be a solid choice in my opinion. I'd have to put my hands on one first, as the 10.5" Bushmaster I held was not as lightweight and manueverable as I thought it would be.