Nice job. You're obviously a machinist. I'm not and wouldn't have thought to attempt that job.

FWIW, when adjusting the nut/mag catch button in guns which come from the factory with metal mag catches and which use the plunger, the height of the plunger should be such that the top of the plunger is either flush with the frame, or just slightly below the frame. That's so the mag catch has the proper movement to both secure and then release the mag with the intended range of movement of the mag catch nut in the appropriate position.

That's in guns which come that way from the factory, though. I have no idea what the depth of the factory plunger hole is, so I have no idea if this would apply to your personal frame modification. Did you call S&W and ask for the spec before you drilled? The folks in either production or the repair center would probably have the specs available.

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Ret LE Firearms inst & armorer