Some years back I bought a nice 66-2 that turned out to have the barrel turned a bit too far. I sent it in to the factory and they corrected it. What they and I missed however, was that the muzzle crown was somewhat egged-out, either from the factory or bad cleaning practices.

After some thought, I went after it with a Brownell's chamfer tool w ith the proper pilot. I had to go deeper than I wanted to clean it all up, but did get it done. Now it has a recessed crown like a Ruger GP-100, but shoots very well. Prior to this I couldn't get it to shoot well at all. No new barrels were available, so it was my only real option.