I cast my own bullets for my 44. If casting just add a bit of tin or linotype, then higher velocities will work just fine without leading. You should be able to get about 1600 fps before worrying about leading.

I have found you can get 300-500 fps more out of a rifle, over the pistol.
Try some slower powders, and go for full case loads.

If shooting a factory load or factory bullet, go with a Hornady XTP. The bullet was designed to be shot at a higher velocity. It was one of the original saboted bullets for ML'ers. It was also designed to open up at a slower velocity. Try the 240's and do not look back. Tom.