Sometimes having a bullet that's too hard can cause leading also. Before you break out your flamethrowers let me explain my point.
When a bullet is fired the force causes it to obturate, or smash out and fill the lands blocking the pressure behind it and pushing it forward. If a lead bullet is cast too hard it doesn't obturate and make a solid seal in the barrel. When that happens the flame goes around the base of the bullet and melts the lead as it escapes basically soldering lead into the lands. When this happens it leads something awful.
I'm not saying that is what's happening here, it could be a number of things. I agree with the post that states 10.5 grains of Unique is a bit much. I also agree you can run a cast bullet of the proper hardness to over 1,200fps.
If it were mine I'd slug it, I've seen barrels that are a thou or two smaller where the barrel screws into the action right in front of the forcing cone. That'll lead em.
Interesting topic, I'd be interested in the final outcome.