As best I remember this-
About 10 or 12 years ago I bought a New 6601, then sold off the top end and bought a new Colt 16 inch flat top upper (maybe from RGuns, but I am not sure). The lower is marked "SPORTER MATCH HBAR:, and has a MH serial number (pre"ban"). The upper is 16 inch, Heavy barrel, marked "CMP 5.56 NATO 1/9 HBAR" The upper has the removable carry handle, short carbine lengthgrips, bayonet lug and swivel built into the front site/gas block. The barrel does not have a step off for a grenade launcher.
The lower was a large pin hole, and there is an adaptor to the upper.
I never shot this guy, and since I figured I would hoard it forever, I sent it to Birdsong for his BlackT coating. And still have never shot it.
Nothing included other than the gun and bolt.
$1200 delivered to your FFL.
Pictures available on request - please do not pm.
Metazorro at yahoo dot com