U.D.,
I hope your friend doesn't go into hiding to avoid hearing "I told you so".
Not having seen the custom barrel or its exact contour, I wonder if the gunsmith simply found too little thread length and remaining metal ahead of the taper to set it back enough for what you suggested? It would be unusual if there wasn't enough thread to set it back a little bit to clean up the 6.5 RUM throat, but given how far overbore that cartridge is, perhaps it's been done enough times already that no room is left.
