I bought 5 CMMG piston driven AR-15 a few years ago. I have 2 left. They are 16" flat top with M4 hand rails. I fixed one up and love it and was going to give the new on to my son when he moved from Baltimore to Atlanta. This is a great platform to build the complete rifle. Right now I think that a PSA would interest him instead of the piston driven gun with a 1:9 twist. The reason CMMG stopped making these guns was because the bottom fell out of the AR-market and piston guns got hit hard even they give you a better option then a DI operations AR.
Google CMMG 55AE1BB to get the specs of the gun. I am not really sure that I want to sell the gun but would rather trade it for a single action 45 LC in a Ruger (maybe 2 cylinders) and a lever action rifle (Rossi would work). Price would be around $1050. plus shipping. I have a FFL and have to ship I would have to ship to another FFL.
I would offer pictures but a AR look like and AR except the gas piston system that works great with a can and if you convert it to a fully auto. It is also cleaner.
If you would like some more interest, please send me an e-mail (RickyFriedenberg@comcast.net) or send me a PM. I an will to travel for the right deal.