I don't know that I would call a 5-6" group unacceptable. If you can get the trigger adjusted, it should shoot to half that. I remember that when I started shooting my Mossberg 500, 6 inches at fifty yards was considered bragging (or lying if someone else told it). Keep in mind that the vital area of a deer is about 9 inches, and that most deer are shot under 75 yards. I personally like Brenneke slugs for full diameter slugs, and they make a one ounce 20 gauge slug that you might try. I am glad to see that you are starting your son out on a single-shot. I began hunting with a single-shot .22. My best friend had a semiautomatic that held 19 rounds. I would bag a squirrel with one shot and he might get one, but he fired 19 times on any squirrel he took. Good luck and good hunting.