Welcome to the forum Form442.

I believe mainspring strain screws do not back out on their own. Often previous owners who do not shoot DA have backed them out to lighten their SA trigger pull and never learned that they made their revolver unreliable in DA. It is also common for sellers to back out strain screws to give buyers the impression that the revolver has an especially good trigger pull. I bet if you just turn it back in it will solve your problem. If it doesn't, first look at the end of the strain screw to see if someone filed it shorter. Some misguided owners do that rather than simply backing the screw out. I have put longer firing pins in moon clip guns but that is not the first thing to change. The longer pins will give you more pierced primers which can be misinterpreted as higher pressure.

Not considering missfires, do you think the PC 625 was worth the extra money compared to your JM 625?

Best regards,

Gil