I was talking with a gunsmith about barrels yesterday and he mentioned a lapping method I hadn't heard about and thought I'd share. He plugs the barrel ahead of the chamber, and stands it on its butt plate. He then puts a slightly undersize brush on a rotating cleaning rod and centers it in the barrel resting on the plug. This is the cool part. He pours a little (just enough) molten lead into the muzzle to encase the brush in the lead. You let it cool, then slowly draw it from the barrel until half or more of the lead plug is protruding from the barrel. You don't withdraw the plug completely because you want it to remain engaged with the rifling. You smear a fine lapping compound around the perimeter of the lead plug and work it back and forth in the barrel, not fully extracting the plug but leaving the lower part engaged in the rifling at the end of the return stroke so the plug stays registered in the rifling. Every 8-10 strokes apply a little more lapping compound. The lapping compound embeds in the lead and makes a perfecty formed lapping plug. Once you're done with the lapping compound he finishes off with toothpaste.

Anybody ever done it this way? I'm going to try it on a couple marlins he's building for me.

It's perhaps the oldest of the common methods. The indexing is important.
Regards, Joe

I spent a lot of time with Boots Obermeyer..he laps all his barrels, but stops at 150 grit...claims diminishing returns as you lap with finer compound.

A guy that once made barrels working for Bill Wiseman told me that 220 grit was the finest they used when lapping barrels.