I did exactly what rcmodel suggested, and it turned out quite well. I could not find a round headed brass bolt sold alone at a hardware store, so I bought the set to bolt the upper tank onto the lower part of a toilet. Using one of the two brass bolts included, it has a slot in the top for tightening with a screwdriver. This will hold more lapping compound. The only problem is that it a slow process. Even with that said, if I live long enough to re-crown 100 rifles, unless I ever were to buy a lathe, I figure I will always use the brass bolt and lapping compound trick. It should work for most any caliber barrel as far as I can tell.