I managed to get one of these, and it matches the condition of the interesting surplus FN uppers (also from Thoroughbred) that are being discussed in the
Interesting FN/Colt Upper Receiver thread, for those of you that are following that conversation. It was pretty filthy when it arrived today, but probably not as bad as a couple in the other thread, and it cleaned up fine. It has the same heavy wear patterns on the anodizing but looks fully functional. The abuse at the rear of the rail where the BUIS was mounted seems a little excessive - not sure what the previous users were doing there, but it looks like maybe they overtightened the mounting bolt (I'm guessing it was a Matech), based on the thread marks on the left end of the rearmost notch in the rail.
The gunk around the gas tube opening looked just like a 6933 upper I disassembled last year that had seen heavy suppressed use. I could probably clean it a few more times and still not get everything out of there. Quite a bit of residue in the forward assist... tube?... as well. The wear on the finish is more advanced than on my last issued M4, which was built in 2003 and assigned to an Infantry battalion, so I'm guessing that if these were surplus military, they were from USASOC or another unit that put a lot more rounds through them than a regular Army line unit. I think it would make for a good salty upper for a SOPMOD Block II or URG-I conversion clone, like a lot of the ones Combat_Diver has posted photos of.
I'm going to have to complete this upper with Colt parts, of course, so I better give Chris at Shark a call. It will add to the cost of this pretty worn upper, but I wanted to see what one of these looked like, and I had to jump on a C-stamped upper when I saw it.
Here are a few quick photos that I snapped after cleaning it, including one of the proof mark, which is always good to see.
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