[RLK]

Well, I know on a lot of rifles all that's needed is to shave down the sheer pin.

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That's an old wives tale. What would happen is the firing pin would slide into the primer. The firing would be haphazard. In a nodern inertial firing pin system you would get nothing. To operate effectively, a fully automatic rifle employs a delay system in which the pin hits the cartrige after the breech is closed and locked.

[Mortimer Snavely]

Thank you for these two posts.