I recently purchased two M16A1 uppers. The first upper is marked "C  K" and the second upper appears to be unmarked except for a faint little triangle stamp towards the front. Both barrels are marked "C MP Chome Bore".  What does the "K" mean on the first upper? Any idea about the second?

Thanks!

Colt / Kaiser Aluminum.

If I'm wrong, I've had 3 beers.

CK uppers are typically found on early 1970's Colt's M16A1's, along with CM.  No forge code XM16E1/M16A1 uppers were used from 1964 till about 1971 or so, and were manufactured in large numbers.  Judging from the presence of the code in front of the port door it is a Colt's part.  These have been hard to find as of late, and if you are interested in selling it you might E-mail me.

Would suspect that both uppers are rebuilds in that CH forge codes and C MP CHROME BORE barrels go together (factory original M16A1 rifles).  CK uppers typically have C MP B marked barrels, and no forge code M16A1 uppers had numerous different markings.  Another hint that a upper came off an arsenal rebuild is a black slip ring.