Match your recoil spring the PF of your ammo. If you're shooting factory ammo, I would suggest staying with the 17# spring (DO get a SS guide rod, though). Going to a 13# spring will leave the gun with less resistance to the slide and will just beat up your frame. If you choose to reload to minor power factor, then a 13# spring is a good idea. If you load to minor power factor with a factory spring, there is a risk of failure to eject.