Cowboy action light loads are pretty light. The goal being about 700 fps. When going this light with a 125 gr bullet, it seems that nothing works. I chased this for a while. The reality is that the 357 mag case is too big. Powder position sensitivity and ignition are a constant battle. I dont like crud rings any more than anyone else, but I got tired of failure. Interestingly I ended up buying some 38 Long Colt cases and loading 125 gr bullets with Trail Boss. At +70% loading density ignition is decent and powder position is within a few fps. Crud ring formation is slow, and even after several cylinders of LC, I still could seat, shoot and extract 357 cowboy loads. Trail Boss responds to primer differences. In the LC a Fed 100 seems good. A CCI SP works in the 38 Spl, and in a 357, most of the time a WSP is the charm. Don't hesitate to change primers if chrono results are not good. And at less than 70% loading density, TB is a poor performer.