There are tradeoffs. One thing to try is a harder lead alloy, since the softer the bullet, the more it will lead the barrel. The second is to reduce the load; the higher the velocity, again, the more lead fouling.
You can certainly lap the barrel. I have never used fire lapping, but have heard good results as long as it is not overdone, but even the smoothest barrel will lead if soft bullets are fired at high pressures and velocity.