The mark is the forge mark, the forge sells to many companies to machine then those companies sell to many more assembly companies. Most companies even big ones like S&W buy many of their AR parts, S&W buys some if not all of their barrels from ER SHAW, their uppers seem to be YHM with the keyhole forge mark, seen the same forge mark on Daniel Defense uppers.
5.56, 6.8, SIX5. The Nexgen of 308s
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