Underwood 200gr 10mm Hard Cast

[4949shooter]

You might want to try a 22 or 24 pound RSA.

You can get them from Glockstore or Glockmeister.

[The_Shadow]

In my G-20SF I use a Non Captive RSA from Wolff, the reason being is it applies more pressure at lock up...

Glock 20SF spring test Wolff Gun Springs 22lb RSA installed
It takes 6lb 4oz to start the slide to move from the locked position
Full retraction at 22lb 9oz at lock open
22-Slightly over a pound difference 1lb 1oz to start the slide to move from the locked position
22-Slightly over a 2 pound difference 2lb 9oz at lock open over factory

Glock 20SF spring test Wolff Gun Springs 24lb RSA installed
It takes 7lb 6oz to start the slide to move from the locked position
Full retraction at 24lb 1oz at lock open
24-Slightly over a pound difference 2lb 3oz to start the slide to move from the locked position
24-Slightly over a 6 pound difference 6lb 1oz at lock open over factory

Glock 20Sf Factory spring test
It takes 5lb 3oz to start the slide to move from the locked position
Full retraction at 18lb 0oz at lock open