I bought a case of PMC 9mm ammo and am getting multiple failures to fire. I am going to replace the main spring as I've had the gun for years and have shot thousands of rounds through it and figure maybe it's time to get a new spring. Anyone know the weight of the spring Sig puts in the 239? Thanks.

Wolff Gunsprings claims 18# is the factory rate.

Wolff Gunsprings as @Chris Orndorff suggests - good folks.

Also check the firing pin for smooth operation: Hold hammer back with thumb with trigger pulled. Use suitable wood or plastic rod to push firing pin forward for a quick check.

Thanks guys. It’s not all the time. Every 3rd round or so. I’ll get a new spring and see what happens. My 226 was doing the same thing so I suspect it’s the ammo but I need to be sure and figure it’s probably time to change the springs anyway.

Visually inspecting the primer indentation should give you all the information you need to determine if the firing pin is impacting the primer with the proper force. No sense replacing gun parts if they are doing the job and it's the ammo at fault.