The Q5 SF cocks the striker in last 1/8" per Imaoldfart @ Waltherforums as it returns to battery. If using reduced power recoil spring, less power to return, thus use reduced striker spring. With a very weak recoil spring (Sprinco white) and stock striker spring, you can get a partial return to battery that still lets you pull the trigger, get a click, but no bang as releasing the sear and striker spring gets the slide to move fully into battery, but the striker doesn't have enough energy left to set off the primer. Had that happen before using reduced striker spring.