[MrMcGoo]

The roll pin functions to retain the firing pin. A similar shorter pin hides under the long extractor of the newer P series. The MK 25 uses the older short extractor, hence the firing pin retainer has to go all the way through.

Bill

 

[drPhibes]

That's the firing pin retaining pin.

 

[Tvphotog]

Thanks, guys.