Quoted:
I have a casting ( C ) Symbols question? 95% Of flat-top I seen come with the Colt ( C ) raised and a very few I have seen come with (C ) Stamped next to the casting symbol . What is the story behind it?
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The original flattop upper receivers, with the "C AF" forge marks were raised "C."
For reasons that have not to my knowledge, ever been specifically articulated outside of Colt, they began switching to the stamped "C" sometime around 2005, though I do not have the exact date on hand. For a while there was a period where both were common and it was kind of random whether you'd get a raised or stamped "C." on modern production Colt upper receivers, the stamped "C" is much more common.
One thing to consider is that in order to have the raised "C" marking, it must be present in the forging die, while the stamped "C" can be put on after forging. Before the global war on terror, only a few companies were building flattop upper receivers, and therefore, by extension, buying flattop forgings, and there could be "Colt specific" dies with raised "C" markings in them.
As demand for flattop receivers became higher, Colt likely started purchasing non-Colt specific forgings, but finishing them to their specs and stamping the "C" on them.
As the older forging dies began to wear out, it was probably much more cost effective to have a single flattop receiver forging made, rather than a Colt exclusive forging, or one where the raised "C" had to be machined off before it could be sold to another finisher, and Colt continues to stamp the "C" marking on receivers that they have finished.
All this, of course, is my speculation alone, there could be a much different answer provided with someone who knows more or better - I'm not necessarily the "forging expert" in the community - I tend to be more or less only concerned with whether or not there is a "C" marking - though I do like early "C AF" gray receivers with no T-marks, but that's the retro junkie in me.
~Augee