Tom, I hope you are not sizing the bullet down to jacketed bullet size. If you are, try them as cast dia. if you can and see what happens.
Also, dont try to drive them too fast, even if its a harder alloy.
You could have some issues with the factory throat/leade/angle; it may be a long slide to it and a not lead bullet friendly angle to enter the rifling.
Work on the bullet dia. thing first and we'll go from there.