I was shooting an old pinned/recessed M57 with a 4 inch barrel. I was surprised the H110 loads were not faster. I might try some 2400. I started with H110 because it seemed that the loading data for 2400 was all over the board from the different sources. The H110 seemed to max out at about 22 grains from most sources. I generally use H110 in .357 Magnum loads and 2400 in bigger stuff. I used WLP primers most of the time. The cases are crimped about as heavily as the dies will allow.
9 grains Unique with 215 SWC lead 1117, 1077, 1100, 1117
8 grains Unique with 215 grain SWC 1039, 1002, 1079, 1048
21.5 grains 210 XTP Hornady 1185, 1145, 1115, 1101
The velocitys as posted for the load using unique arent that far off for a 4" barrel. Powders I have used in the 41 range from Red Dot, unique, and W296. You might be over belling the brass, had this happen to me on a set of dies. The belling die was mis cut, going to deep in the brass. My favorite 41 mag is AA #9. mild to Hot loads are no problem with it.
Good luck
Swifty
