I would try .0575 or .057 round ball. I hunted elk for about 10 years, bagging 7 elk. when my eye was healthy. I never lost a elk. I used either a 50 or 54 cal. gun. My normal load for the 54 was .530 round ball, heavy patch ( pillow ticking ) with good coating grease. and 90 grains of 2ff. The 50 cal was 90 grain 3fff and .495 round ball with pillow ticking patch. All the elk I shot were closer than 100 yards (80 to 5 yards avg probably 50-60 ). I used either boughten swedged round ball or moulded my own. I weighed all the moulded balls. I remelted any thing that wasn't close to the avg.