There is plenty of published data for "max for maxi" loads, using W296, H110, 4227, and 1680. All of these give velocities higher than I am looking for. I can't find any data for a 1500 fps cast bullet load.
As a starting point, I figured that the maximum load of Unique in the 357 Magnum for that bullet weight would be safe in the bigger Maxi case. I fiddled with the numbers a little and drew a chart, comparing how case capacity in cc of water and charge weights for Unique with 158 gr cast bullets varies from 38 Special, 357 Magnum, and extended the graph to the Maxi using the case capacity and seeing where the unknown Unique charge weight would fall.
Please note here, I DID NOT just use my numbers and start loading tablespoons of Unique into Maxi cases. Instead I used the old school cut-and-try method, inching my way up by tenths of a grain from the 357 mag load. I finally reached a charge weight that chronies at about 1400 fps, has decent 50 yd accuracy, and that has very mild looking primers and no case head expansion that I can measure. This load also sounded right. Lower charges had kind of a hollow "pop" sound to them, but the final load just gave a normal, moderate "bang".
BTW, the load ended up being almost exactly what the math predicted, haha !
SO- Hey Mrcoolid, what was your source for your load using 19 gr of 2400 for the Maxi ? I recently got some 2400, and was disappointed to find no data.