11BHN is softer than wheel weights. I suspect anything over 900-1000 FPS you'd run into leading problems. I'd recommend only loading to .44 Special velocities with those bullets. Hard cast will give you a little more FPS before leading problems develop. If you use GC bullets you shouldn't have any problems. Bottom line is using cast bullets in a magnum caliber is tricky and if you want real magnum velocities using cast bullets you are religated to GC bullets.
Cast bullet reference on lead alloy's, min / max pressure, lube, shrinkage,