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Old May 27, 2010, 01:21 PM   #10
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Join Date: June 9, 2002
Location: northern CA for a little while longer
Posts: 1,883
The standard AR-15/M16 firing pin protrusion gauge recommended in my Colt & S&W M&P 15 armorer manuals uses a GO dimension of .036" and a NO-GO dimension of .028".

With the firing pin held firmly forward in the bolt, the end of the firing pin protrusion gauge (or gage, if you prefer) marked "MAX" (GO - 0.36") should pass over the end of the pin without touching it, and the end marked "MIN" (NO-GO - .028") should hit the end of the firing pin and not pass over it.

Just out of curiosity, how are you measuring the .026" protrusion, and why not simply use the appropriate gauge?

FWIW, I've yet to check an AR firing pin with the standard protrusion gauge and have it fail to exhibit the proper protrusion. If I ever do I'll replace the firing pin with one that passes the normal check.
Retired LE - firearms instructor & armorer

Last edited by fastbolt; May 27, 2010 at 02:46 PM.
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