You should be able to determine if you are holding a 1st or 2nd? gen gun in your hand by turning gun upside down with action closed (slide forward) There is a lug soldered on to the mag tubes, behind this lug there will be a small notch at the very front of polymer lower receiver. If you are holding a 2nd? gen gun you will see a small tab of metal in that notch. What you see there is the forward tip of the "cartridge stop actuator".




























