If you compare the grooves just above the rim the difference between M2 Ball and 7.62 is quite obvious. My personal opinion backed by nothing substantial is that the Izzys gaged the bolt if it failed the opening to the T slot and slot were modified and the bolt stamped 7.62 if it passed they just stamped it
Greek HXP M2 Ball has both styles of grooves depending on year of manufacturer and I have some M1909 .30 cal blanks head stamped LC 12 (2012 production) that has the different style groove
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