I'm experimenting with handloads for my Glock 20. 10.6 grs of 2400 under a 200 gr no-name JFP from Midway and the slide shut on an empty magazine. This would be when you get a stronger recoil spring, right? There were no signs of over-pressure, (bulging case, flattened primer), on the, (Star-line), brass. Even though it often becomes projectiles itself. I'm using a Lone Wolf after market 4.6" barrel. I did shoot some pretty hot HDY XTP 180 gr loads at the same occation without experiencing the same phenomena. Switching back and forth between the two the slide did shut on the 200 gr every time. But not on the 180 gr.