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Looks nice. Try and find some period correct 7-round mags for it.

 

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One question, is the pin that holds the trigger have the single slot like a flat head screw or is it serrated with multiple cuts?

P220's have the serrated trigger pin.

 

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The slot makes sense on the other P-guns to align the trigger pin for locking insert installation. I have no clue why the P220 is different. I've only completely disassembled my P220ST once (purchased used). I really can't remember how easy (or hard) the locking insert installation was. If I remember I pinched both sides of the pin with my thumb and index finger, and pivoted it that way.

 

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That looks fantastic.