Have the same M12FV in .223.
For the Hornady 55 grn SP I am currently at 1.840 using the same Hornady comparator. Ogive to base. About 2.205" base to tip. Though I don't endorse this measurement as an optimum jump for accuracy by no means.
Have 69 grn Hornady BTHP ready but have been stumbling through other problems and nowhere even close to even moving on to another weight.
Hope your not having the same problem I did with finding the lands, having very short leade and 'bottoming out'. Sent mine back to the factory. Since it's return, the accuracy continues to decline.