I tried 22.5 grains of MP 300 and had very hard case extraction, I went down to 20.5 and everything was OK.While the jkt bullet is lighter, the cast bullet usually runs at a little less pressure so you can often use a little more powder. MP 300 is said to be like W296 but I think it may be a tad slower if anything. I would start a little lower, whatever the manual says if it does, then work up for accuracy keeping an eye on anything that looks suspicious. You cant really use the old rifle pressure indicators like primers because of the lower pressures involved, so it pays to be cautious. If you start getting craters or real flat primers, you are probably on the ragged edge.