To me, there is a point of diminished returns when it comes to powder charges. You will find as with most projectiles, there is one point where accuracy is the best. If you add more powder the accuracy will fail or less powder and you might not get as good.

The trick is start low and work up. With most sabots I start at 80 grains of powder and start shooting groups. That's one reason I am not a believer in getting too excited about scopes and sights until I have the actual load worked up. If you have a good load at 80 grains, move up to 85, 90, 95, etc.. at some point the accuracy will get better or worse. That is the point you want to reach. Or you might come to a point where you do not like the recoil anymore if you are sensative in that area.

If all your looking for is velocity, then you need to get a chronograph. Start shooting and adding powder. There will come a point that even if you add more powder the gain in velocity is not worth the increase in powder. That's diminished returns.