In a striker fire pistol why do people increase and decrease main spring power if there are no jams or other problems?

Personal preference

I shot a DA/SA when I was competing, and I used a lower hammer spring to drop the DA trigger pull weight. I compensated by increasing the slide spring so the slide didn't beat the hell out of the frame.

OK more specific question. Sig has provided me with two springs in my new pistol but doesn't explain why one would be preferable over the other.

One 14lb one 12lb.

With the 14lb spring it shoots great with 115 gr 9mm but if some function of the operation would benefit from the 12lb spring I would like to know.

You said striker fire, but mentioned mainspring, which is the term typically used for the spring that pushes the hammer on a hammer fired gun. Did you mean recoil spring?

The weaker recoil springs may reduce muzzle dip. Also with heavier bullets, or lighter loads, it could reduce the recoil and improve reliability. The last reason for a lighter recoil spring is if the gun has a compensator.

I have messed a bit with reduced recoil spring (12lb) on my M&P, but run the factory spring because the slide would not always go into battery, or it would come out of battery when I seated a fully loaded, extended magazine.

Mess around with the springs; try the 12# on 147's and 14# on 115 gr and 124 gr ammo.

BenderRodriguez said:

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You said striker fire, but mentioned mainspring, which is the term typically used for the spring that pushes the hammer on a hammer fired gun. Did you mean recoil spring?

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Yes

With the load you normally shoot, a different spring may aid the gun in returning closer to where you had it aimed after it cycles. For example, with my CZ Shadow 2, for *me*, a heavier spring caused the slide to return into battery too hard (, causing the muzzle to dip (which I would have to correct for follow up shots). Moving to a lighter spring caused the gun to return much closer to where it was aimed when the gun fired, allowing me to fire follow up shots more quickly. It's all personal preference and tuning the gun to your preferences.

NOTE - too light of a spring may cause your gun to fail to go into battery consistently when it is lubricated less, if the case is slightly larger or dirty, or if, for example, your thumb presses against the slide when you grip the gun.

Madman said:

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BenderRodriguez said:

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You said striker fire, but mentioned mainspring, which is the term typically used for the spring that pushes the hammer on a hammer fired gun. Did you mean recoil spring?

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Yes

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Okay, just wanted to make sure.

Lowing the main spring weight on a hammer fired gun can improve the single action trigger pull, as long as you don't go down so low that it won't reliably ignite primers.

But changing the recoil spring rate is, as AustinAg96 said, more about changing how the gun behaves under recoil.

Companies tend to lean towards "overspringing" from the factory to make sure their gun will run whatever crappy ammo people put through it and be reliable.

You can go lighter than factory and it MIGHT improve how the gun handles when shooting at speed, if you're an experienced enough shooter to notice a difference in how the sights return to target during recoil, and you're using ammo that doesn't need a stronger recoil spring to return to battery reliably, etc.

If you want to swap out to the 12 and see how it does with the ammo you're shooting, there's no harm in it.