Strange mark on Diemaco upper

AR/M4 AR Technical Discussion
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Hello all…first post here. My new 6920 Diemaco upper has a strange mark on the right side that’s forward of, and a little higher than, the ejection port. It doesn’t look like any kind of intelligible symbol, but it looks deliberate just the same. It looks like it was made with some sort of punch (almost looks more like a small chisel mark) after the upper was anodized. I could have sworn I saw a picture of another upper just like this on this forum or the other one awhile back, but I can’t find it now. I think the posters decided it was something particular to Diemaco…perhaps a hardness test they perform on every 100 or so uppers (just a number I’m throwing out there). Does anyone else have this mark on their Colt upper?

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First off…Welcome!
B., pictures are worth a thousand words.
5th, check HERE for the Forge Marks Knowledge Base

BTW - NOT trying to be harsh, just comical. FWIW

3

Thanks for the welcome…let’s try this…

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Here is a little image help…

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Thanks for the help. I think I must have seen the other upper like mine on the “other” board. I’m not a member there, so I can’t see posts behind the first page. If anyone has access to the Colt forum over there, maybe they could search for “Diemaco upper” or “Colt upper”.

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It’s just a proof mark as far as I know. That’s how they’re always referred to anyway. All the colts that I’ve seen have them. Military uppers that I’ve see have 2 different markings. A “c” inside of a triangle and such.

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Thanks Markm!

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Could it also be the results of a hardness test as well as a “proof mark”?

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I think demigod’s proof mark explanation is the most plausible. I’ve never heard of peening aluminum to test for hardness in firearms, but proof marks aren’t that uncommon…German pistols especially come to mind…older Sigs, Walther P5s, etc. What’s strange to me is that, while most proof marks look like “something”, this one just looks like it was put there for the sake of putting it there. I guess it kinda looks like a “D”, but not really.

10

I went and checked my Colt last night. One of the markings actually has a “c” in a square, and the other has some other markings in a triangle.

I’d guess that they’re stamped on the guns in final inspection processes.

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I checked my Colt last night as well, and if I understand the OP’s description and related photo correctly, what you have there is a ding mark of unknown provenance. Or a super-rare backwards-swoosh Nike upper.

12

I’ve got a similar proof mark on my '04 6721 Diemaco upper.

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I have the very same mark on my 6920 Diemaco upper at first I thought it was a scratch but after asking around no it is a proof mark. I think its kind of neat.

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I think it’s hella neat :slight_smile:

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This is a pic of a issued Canadian C1A1 FAL… Look familiar???

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A little help for those that aren’t logged in to the FALFiles :slight_smile:

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I just noticed another similar mark on the receiver just behind the carry handle bar…too bad it’s in the way.

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A hardness test or “Rockwell Test” will leave a small round indention usually either 1/16 or 1/8 in diameter depending on the aluminum type and hardness.

Just wanted to add that bit of info.