So I stumbled upon one of the AAC 12.5" BLK URX uppers a couple of years ago for $500 NIB and couldn't pass. Turns out, I shoot my 9" BLK upper way more - obviously. Anyway, I'd like to stick a 5.56 barrel on the thing and was wondering if anyone has experience swapping barrels on these. I went ahead dropped the $115 on a barrel nut wrench and bought one of the tool steel barrel nuts if needed. Is there anything else I need to be aware of? Any opinions on 11.5" barrel options?