If you have a mossburg 500 why not use it for coyotes. There are alot of options for shot sizes you can use. the 00 buck will definitely bring them down, but pattern density is limited.I prefer #4 buck or slightly smaller. Something in the T, BBB, BB, or 2 shot range is great for coyotes. Hevi shot dead coyote would probably be your best bet. I would stay away from the .22lr. Good luck!

http://www.hevishot.com/products_dead_coyote.html