The Gen 4 17, 22, 19, and 23 feature a dual spring setup. initially the 17 and 22 had the same recoil spring weight and the 17 suffered some reliability issues. They reduced the weight in the 17 springs and the 19 springs. That being said some shooters are still having issues with the Gen 4 19, my wife has one and while the gun was more reliable than not, it had a few issues. We replaced the recoil spring assembly with an aftermarket kit that has the same single spring/weight as the Gen 3 Glock 19 and the gun hasn't had a problem since.