Pattern a good slug with his gun and have him keep the distance within the range that he can keep them all within a paper plate. IMHO buckshot is strictly for a seasoned veteran that will keep his shots very close with the knowledge that they will wound more animals than they will kill if the distance is stretched to any extent. Make sure he has good hearing protection, as well as a properly fitted gun with a good pad. Then start him out pretty soon working him on up to those loads, as they are a lot more potent than what he's been shooting and he'll quickly realize that when he touches the first one off.