good gun. i haven't shot the 500, but i did hunt with an 835 for 2 seasons. i abused that gun. rarely cleaned it, usually got tossed around the bottom of the boat (unloaded) and gear would eventually get piled on it...wet muddy dogs would sleep on it..and yet if fired everytime i pulled the trigger.
i did have a problem with the ejector screw falling out occasionally.
open the action and look in..the screw you see is the ejector screw. i would check it every time you clean your gun to make sure it is tight. the problem with mine was that the hole for the screw was slightly out of round. factory defect. my gunsmith was even surprised that i had that much trouble with it..as far as he knew mine was the only one he had ever seen with that problem. so don't be worried about it.
congrats on the gun. is it your first? i think you are going to love it.
Friends Don't Let Friends Shoot Mossbergs.