It was with the Gen 3 guns the extra pin was added and the chamber was given more cartridge support.
Gen 5 increased slide weight through increased dimensions.
The Gen 4 is where GLOCK addressed the recoil impulse of the .40, among other things, by abandoning the flat wire single spring in favor of the dual spring on compact and service models.
It was initially a little over-sprung for the std. pressure 9mm, and resulted in a lot of BTF issues.
GR
