Thanks for the vid. It confirms my theory that the shelf difference is for seating the new RSA, however as people have posted on other forums, this position is null after the pistol is assembled... Which would explain why everyone who has posted that they are using a Gen3 barrel in a Gen4 gun has had 100% reliability. I will have to put that theory to fact myself next weekend, as I have just won an auction on a Gen3 G32 barrel for my Gen4 G23. I will be running the 200 rounds I have of WWB .357sig to ensure it works. Results will be posted here. Hope I don't break a wrist... Wanna kill these ads? We can help!