Kinda doubt a lapping compound would embed well into a brass bullet. At least not well enough to do the job. Too hard a bullet and you will get inconsistent lapping. You will want a bullet with a good bit of bearing surface. If that Barnes Expander was wheel weight lead it would actually be PERFECT. After around 20-25 ML barrels lapped and I don't know how many CF rifle barrels, I kinda have it down pretty good. Best lapping compound I have used so far is Clover Lapping Compound. Get the "Fine" grit, I think it's CL.1A 320 grit. You can find it at pretty much any Mechanic Supply (never tried Auto Zone but I don't consider them Mechanic supply). It has seemed to do the absolute best job for me. After I fire lap I will run a 100-150 strokes of JB just to mirror the finish. I've brought several rifles back from the dead doing this. Some were on the brink of becoming fence posts!

If he's gonna shoot sabots the crown is good enough. In my opinion, I like rough bores. It allows less sabot slippage in the bore. If he's going to shoot bore size bullets it might need some work yet.