Have a glock 35 thats been perfect for more than a year of 2-3x a week regular shooting, until yesterday...installed a 22 lb recoil spring from ISMI then after 58 successive rounds the slide cracked in the breach face such that the firing pin hole was enlarged to 3x its orig size. maybe due to excessively strong spring pressure when the slide returns to lock-up. and the breach absorbed most of it. maybe. Can anybody think of any other probable cause? Glock is perfect. we dont need after market parts and accessories such as this. or glocks are deffective that they cant durably function w/ this parts. Either way, BEWARE!