US patent number US3830500 http://www.boardgamegeek.com/image/340548 Take steady aim http://www.boardgamegeek.com/image/181966 http://www.boardgamegeek.com/image/76050 http://www.boardgamegeek.com/image/56896 http://www.boardgamegeek.com/image/26528 http://www.boardgamegeek.com/image/26344 http://www.boardgamegeek.com/image/26342