How often do folks replace their firing pin springs?
I know weak ones don't detonate primers good enough to produce small muzzle velocity spreads. Most modern centerfire rifles' springs are rated around 23 to 25 pounds when cocked. One can go to:
Wolff Rifle & Shotgun Springs
then use the table on the left side of that page to find out what their rifle's factory spring's rated at.
There's little difference in the force load between cocked and fired length when the spring's in the assembled bolt. And a constant load compressing a spring tends to weaken it. How much depends on the metalurgy and treatment of the spring.