I have a Colt M4 post ban upper. The rifle it came off of was a model MT6400C.
History on this is I traded a FAL for this Colt rifle new in box about a year ago. As soon as I got it I sold the Colt lower and put the upper on my match grade Bushmaster lower. This upper then had 100 rounds fired out of it and has been waiting to go to ADCO to have the break taken off and a FH put on. Just never got around to it and now I have a Bushy M4 upper too. I don't need both and to me an AR is an AR, I don't care who made it as long as it's one of the better manufacturers and I know I can get more for this Colt.
Anyway, I don't know much about this upper. It is 16" and chrome lined with that big muzzle break. Very accurate. I'd call it 95%+ condition. I have a pic below that shows where I scratched a little black off the handguard ring holder when trying to put a RAS on this. Hardly noticable but you can get a new one for it. I would guess they are only a few bucks.
599.00 shipped. Will listen to any trade offers too. IM me here for quick reply or you can email too.
Here's the pics: