Thanks Troy. I was afraid of that. I did go back to look at the carbine again, but in the end I just decided against buying it. I field stripped it to see if I might run across some markings on the bolt carrier assembly or inside the upper receiver itself, but I could find nothing distinguishing at all. On top of that, this closer inspection also revealed another problem. The only way to remove the rear takedown pin was with a damn brass mallet and a drift punch! I never saw a pin so tight. One thing is for sure, the fit between upper and lower was definately tight enough on this carbine to not require any of those aftermarket gadgets! LOL. But I assume something was pretty out of spec to cause this, so I chose to pass on it. I didn't really need it, but thought that at $600 it might make a good new addition. However, I have rifles I trust and don't want to take a chance on getting a piece of junk.
While being able to build your own AR rifles from kits has certainly made it cheaper to own an AR, it has at the same time destroyed the used rifle market. There are so many of these floating around anymore that unless it is specifically marked, you have no clue what you are getting. It should be a requirement that the manufacturer and twist rate/chamber be stamped on the upper somewhere. Otherwise someone could buy a kit, build a lower with whatever marking they choose and later sell it as a Colt, Bushmaster, etc for a price far in excess of it's worth. I am amazed at how this practice can be allowed. I am sure many people who were caught unaware have been ripped off in this manner.
-Charging Handle