After spending a few thousands on various 10mm ammo including the XP while testing my glocks I finally gave up and sold my 10mm glock stuff. I think @Clusterfrack is correct about the magazine springs; however, I don't think I want to go down this rabbit hole again to test and verify it. A few hundred rds through such a heavily modified pistol may be not a sufficient sample to draw a conclusion. IMHO... I really hope SW will make a better pistol.