I have a brand new Glock 20SF that fails a check of the recoil spring assembly. I didn't care as I have no intent to shoot it with a factory recoil spring assembly but just thought I'd mention it. If you are getting a Glock check that out. The procedure to check one is (with an unloaded gun magazine out) pull the trigger and hold it back, hold the gun strait up, retract the slide fully, ride the slide forward as in release it very slowly. If the recoil spring assembly is good the gun should still full close. This is how they teach you to check it in the armorer's class.