I saw a man at the Wardlow Alberta full auto shoot once take a 1928 Thompson for the long shot. He went prone, tied up in the sling and ran the Lyman sight up to about 500 or so. He fired single and it took several to get on but he did hit it and get the gong swinging. We could hear the hits at that distance so it still would have hurt! Is your HK full or semi only?