There are various Colt upper markings, "C M", "C AF", "C MB" and probably others.  I know this generally means where (as in what company made the upper) the upper receiver was forged, but does it mean anything about the application or use of the upper receiver.  For example if I had an upper receiver with "C MB", would this imply that this upper was used on an M4A2 upper receiver assembly (I also know that generally M4 uppers are stamped near the gas tube port)?  Or is just a random, receive them at the factory and mate them with whatever barrel assembly is coming down the assembly line?  Thanks for any help and info provided.

I believe it is only the company that made the forging.

This site might help ya out: [url]http://www.biggerhammer.net/ar15/[/url], they have good Colt info...

Mike

Apprecaite the info.  biggerhammer.net has a lot of info and it is very hard to sift through.  Haven't found much on upper receiver markings in the Colt Variants section though.  Maybe they are meaningless as to the type of rifle they go on.  Reason for info need is I have a "C AF" and a "C MB" upper receiver that I would like to complete into full upper assemblies and would like to be accurate as to application, if possible.

Purely a question of what forge was cranking out the pieces that week, or month or whenever[:D] Colt did use different forges at different time periods. For example, I have an A1 milsurp upper marked C K, and I know that Colt didn't start using Kaiser produced forgings until toward the very end of A1 production; but that's about all I can tell.

Put your uppers wherever you like them best, or whichever way they match up best with the lowers you're using.

One more Colt upper receiver related question - Is there anything special about the upper receivers that are stamped "COLT 223" on the side opposite of the ejection port?  Thanks for the info.

Just an (educated) guess, but I suspect that upper was part of a barrelled upper assy meant to swasp back and forth w/ one of their 7.62x39 uppers.  given that colt could expect the uppers to be swapped around, and the lower wou;d be marked 7.62x39, they marked the upper w/the .223.

That is correct - the conversion kit uppers were stamped with the caliber.  As with all things Colt, there are no absolutes, as I had a 6731DC conversion upper that was not stamped.  But most of them were...

Thanks for all the info.  I see alot of these upper receivers for sale with different markings, usually advertised as "Rare, one of a kind, experimental, special forces version, etc.", and I was wondering if they were something worth owning or is this person blowing smoke to sell their item.