Spring InfoBack to Kel-Tec stuff
I actually had shortened my FP to keep light strikes away because I shortened and lightened my trigger pull (so to make up for the lighter hammer strike, I lightened the FP spring to ensure the FP hit would still be sufficient).
Then wondered about drop fires, and when I tested it out was very surprised at the results. So then I actually tried the Wolff 5% extra power FP spring and that improved the drop fire distance (which was further improved by the V paperclip hammer spring mod). But doing this has the possibility of introducing light strikes, so I removed the FP and smoothed it, the FP spring, and the FP set screw, as well as champhered the fp hole on each side by hand with an oversized drill bit to help keep out dirt. I have one of the lightest and shortest P-11 triggers with the extra power FP spring and still don't have light strikes, so I know it can be done.
The 10% extra power recoil springs will help reduce felt recoil a bit, and help in overcoming slide friction to chamber the next round. It should reduce the battering on the frame from the slide contacting it at the end of it's rearward travel during cycling, but may increase the stress on the frame when it returns forward. The latter is less of an issue to me because it is also feeding a round which slows the slide down before it comes to a stop, plus I like positive feeding, and knowing my recoil springs have the ability to overcome a slight lack of lubrication or dirt/grime buildup.
Recoil springs, mag springs and round recoil (term I just made up affected by both charge and projectile weight of the round you are firing, weak light loads may need different springs than strong heavy ones) are also kind of a balance. Go to strong on the recoil springs and if the mag spring is not up to par, the slide will slam shut without chambering a round, or the nose of the round will hit and getting stuck on the bottom of the feed ramp because the mag spring did not pop the top round up fully into position fast enough. Go really overboard with the recoil springs and the slide may not recoil back fully to properly eject the spent casing.
Mag springs if too weak may not pop the round up fast enough to get it in front of the slide before it slams home leading to feeding problems mostly at the end of the mag. If to strong they usually lead to feeding problems at the beginning of the mag (one of the first few rounds) because too much force is needed to strip the rounds from the mag.
ok with all my theories out of the way here is exactly what I have found to work and not work in MY KT's
Wolf 18 Lb extra power recoil springs with stock KT 10 round mags, and original S&W 12 and 15 rounders with 10% extra power mag springs, Wolff 5% extra power FP pin spring (smoothed FP, spring, and FP set screw).
Wolf 11 Lb extra power recoil springs, stock KT mags, KT mags with +1 extension and stock spring that comes with them. With the 11 Lb extra power recoil springs the stock 10 round mags from KT did not function well, I believe the mag springs in these were to weak to function properly with my stronger recoil springs. I never tried them with the stock springs, and the mags were only intended for range use and as of now no one offers stiffer springs for them, so I just sold them.
Here is a link to the Wolff gun springs FAQ page.