Stock spring will work just fine, and I recommend trying it stock first. If you start getting very wide deviations in your rounds' velocities it may be because the stock spring is allowing the slide and barrel to unlock too soon, in which case a stronger spring will help. It also helps with frame and slide battering, but I've never heard of someone with a problem due to slide battering...A stronger spring will also keep your brass from getting slung into the next county. I run a 22lb ISMI spring on a lwd guide rod in my g20sf, and it has been perfect, even the weak, cheap, steel-cased tulammo brand .40sw rounds cycle it just fine. Personally, I wish I had bought a 24lb spring, and I recommend you buy a 24lb spring also. A lot of guys will say that it is too heavy, and they may be right, it just depends on your gun...Still, I promise that any 10mm load you run in your gun with a 24lb spring will cycle your slide, (other than maybe hand-loaded ***** fart loads).
Glock 20SF Gen 3
Glock 27 NiB-X Gen 3
Glock 19 Gen 4
Spike's Tactical Enhanced CHF 16" Mid-Length M4
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