What chamber do you actually have? Is it a 223 or a 5.56 match chamber? The 77SMK is designed to be seated deep and feed out of a standard AR15 mag. The 80SMK is not and it requires a 5.56 match chamber. The throat is substantial longer in the match chamber than the standard .223 chamber. That said your .223 chamber might have more throat that the Krieger .223 chamber which is the chamber in my AR varmint rig. Very short throat.
Best regards,
Grit
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