Is there a definitive 'source' for markings on upper receivers and bbls. that verifies manufacturer?
 I've never paid much attention since I built/re-configured from Colt parts, but I'm pretty disgusted with Colt and want to use other sources[probably largely shared anyhow]. Stuff like 'C  MP 5.56 NATO  1/7' is pretty self-explanatory, but a 'c' and 'H' below the windage disc on an upper isn't.
 Don't recall ever seeing a makers name on a bbl. or upper.
 BTW, how's the quality rated on DPMS chromed bore M-4gery 1/7 bbls. on their flat top? TIA,Ghost

C and H on the upper, indicates that it's a Colt made part with the raw forging produced by the  forge that uses the letter H for ID (I forget who that is right this minute and too lazy to go look it up[:D]).  To my knowlege Colt is the only one that has ever marked their uppers this way.

Bushmaster marks it's barrels like Colt, except they use a B instead of a C, but none of the other aftermarket manufacturers do. There are also some government contract M16A1 barrels floating around that have markings similar to colts, except that they have their government contractor ID number on them instead of the C.

Non Colt uppers usually have only the marking of the forge that produced the blank for the maker, and are found on almost all of the aftermarket pieces.  For example, you can find the split A (Anchor Harvey) forge mark on uppers put out by just about every aftermarket brand out there, and there are several others as well.

I used to recommend going to the Bigger Hammer web site for ID info on uppers, but the site hasn't been updated in two or three yaers and the info is so out of date as to be almost useless for IDing anything built lately.