After playing around with it some, I have decided we'll need a brand new firing pin. It won't be just a longer pin, either. A few additional changes will be necessary:
- The original pin is a thicker diameter than both AK-47 and -74 style pins. The RPK style fluted pin is close to the thickness.
- The pin needs to be the same length as an AK-74 style pin. 3.380" long to be exact.
- The pin retainer hole on the PKM bolt is located directly through the center of the firing pin hole. Compare that to an AK bolt where the pin is slightly off to the side to clear a "normal" flat firing pin. Therefore, a slot will need to be milled into the center of the pin if that conventional AK-style retainer pin is to be used. Otherwise an FNC-style "captive" firing pin may be a consideration.
- The bolt is thick enough that additional space for a spring could be created, for the sake of a spring-loaded firing pin.
I'm not sure if the primers on surplus 7.62x54r ammo is sensitive like commercial ammo or if it can withstand a free-float firing pin design. Since the PK fires from open bolt, the design is not free-float and blocks the pin from contacting the primer until the bolt is in battery. Kinda like the spur on the AK bolt, but kinda in reverse. I'm going to proceed with the assumption that a spring-loaded firing pin won't hurt and just expect to incorporate that into the design.
Any thoughts on free-floating the firing pin vs. spring-loaded?