IMR 4198 is an often over looked powder in the Whelen with cast bullets. I have a 358318, 358315, and a custom mold that dumps 255+ grain #2 alloy slugs. Had an opportunity to pick up a 358009 a while back but by the time the auction closed it was $140, which I didn't have at the time.
I gas check and pan lube with my own mix (wax ass gasket, paraffin, grease, and a crayon) and run them over 35-40 grains of IMR 4198. Velocities of 2500+ with the 245-255 gr is easily attainable and I've never had issues with lead fouling during summer or winter weather. Accuracy for these is minute of elk out to 300 yds, although I haven't used them for that purpose as yet, I tend to stick with conventional condom wrapped bullets for hunting.
