I absolutely reload brass fired from the stock G20 barrel and have never had a problem like you describe. I'm assuming that the brass you're resizing isn't glock smiled, right?
What dies are you using? I usually use a Redding carbide die, but I have also used the Lee carbide die, and I haven't had this issue. Ever.
Try measuring your fired case head diameter just above the extraction groove before resizing. For Starline brass, that will measure .422" before firing, and after one of firing a full power load should still measure less than .424" Resizing won't reduce that diameter unless you run the brass through a pass-thru resizer. If it's bigger than .424" after one firing, then you might be getting excessive pressure with that load, and that would make sense that you are getting a ridge after resizing.
A handgun is only good for fighting your way to a rifle.