My G20 gen 4 functions flawlessly have been firing target ammo as well as numerous underwood selections without issue, it is completely stock as of now, I have ordered a Rachis recoil system and both 22lb and 24lb springs as the stock RSA allows for some frame battering, have also ordered aftermarket barrel because of increased chamber support though it does not seem to be too much of an issue on the gen 4 I get slight case bulge but no smileys and the bulge is not substantial