3rd pin frames became standard in ALL calibers somewhere in the early/mid Gen3 guns. There are some 2 pin frame Gen3 9mm's out there. Yes, 3rd pin frames were being found in earlier Gen2/Gen2.5 G21/G20's and in the subs. I've owned Gen2 G23's both with 3rd pin and without.
Still searching for a "holy grail" gun, a Gen1 G19. A rare bird.
Gen2 - No finger grooves or rails.
Gen2.5 - Finger grooves, no rail. Smooth finish between finger grooves.
Gen3 - Finger grooves, rail.
Last edited by WTM45; 07/22/16.
