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If I might ask, why would more powder make a difference? Might a slower burning powder be something to look into?
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More powder means more pressure and more velocity. If your bullet is undersized at all, you will get severe leading (as you have described already). With a very hard cast bullet, high velocities will cause it to "skid" down the barrel, rather than allow the rifling to grab ahold of it and spin it. As it skids down the barrel, the rifling will strip lead from the bullet. The bullet will also not "obturate" (expand to seal the bore) and that will result in the flame cutting of the bullet as well.
You typically want your bullet to measure .001-.002 over groove diameter for good seal. If you are using a Lee Factory Crimp Die, make sure you have it set to just barely remove any flare you put on the case mouth to facilitate bullet seating. If the FCD is adjusted to put too much of a "crimp" on the case, it can swage the bullet down to where it is undersized. To see if this is happening, pull one of your bullets you have loaded and re-measure its diameter. It should still be the .001-.002 over groove diameter. Most 9mms that I have heard about prefer the cast bullets to be sized to at least .357" and often to .358". As long as they chamber easily, there is no problem with going to those diameters.