I've heard to get desired velocities with the more powerful 10mm loads that it is often recommended to get a 22 lb recoil spring with a Glock 20. Anyone know if the stock Glock 40 recoil spring is sufficient or is there a heavier spring available yet? I don't own a Glock 20 but did recently buy a Glock 40 which I love and intend to shoot heavy loads through.
Glock 40 slide is lighter than the G20. So yeah. If you were to be shooting loads too hot for a regular spring, you would probably need at least the same weight spring in the G40, if not a little heavier.
I doubt you are going to find a commercial load that is too hot for a G40 stock spring, though. At worst, I'd think you might wear out the stock spring a little faster than normal. At the price of those boutique rounds, you aren't going to notice the cost of a spring every year or two.
A recoil spring has no bearing on the velocity of a cartridge.
Agreed. It might change velocity a few fps, or something. In a recoil-operated pistol, the recoil spring affects the maximum loading it can handle and still function as intended. So changing the spring won't make the ammo shoot faster. It will allow firing of faster ammo, in some cases. Same basic reason why sticking a stiffer spring and a muzzle brake into a 1911 will allow it to shoot 460 Rowland. It's not a stronger chamber that makes the gun into a 460. It's the slower slide movement allowing the hotter ammo to extract, and for the gun to not shake itself loose.
You are more likely to cause failures to eject than you are improve your velocities much.
You will want to increase the spring to fix failures to eject. If your ammo is too hot for your gun (and the gun doesn't blow up), it will fail to extract. Stiffer spring will fix that problem. But if you're at that point, you're usually talking about handloads.
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I've heard to get desired velocities with the more powerful 10mm loads
Probably more accurate to say that to get desired reliability with more powerful ammo, you might want to change to a heavier recoil spring. Shoot it and see.