This is a new-in-box Colt M4, model 6400C. It is a flat top with carry handle, side sling adaptor and law enforcement-type pinned on muzzle brake. I believe the barrel is chrome-lined. The lower is also marked M4. This M4 came from the factory with the standard A2 stock. If you like, I can replace it with an M4 stock (non-Colt) fixed in any of the six positions available. Comes with all the normal Colt goodies (cleaning kit, magazine, sling and manual). $1150 shipped to your FFL.