Imo retumbo is to cold for bullets less than 200grns, you will use over 100grns of retumbo with a 180 most likely and can accomplish the same with about 12grns less Imr4831 or 9-10grns less with 7828 or H1000 plus you will have a tighter ES by not using retumbo, but if you must you will probably use about 102grns, starting at about 96-97.