[quote=Der Ami] gunman,
There is no need to take them apart, in fact, it is important to keep them together, to maintain the convergence. They should be reamed, while full length( running the tailstock center in the barrel being reamed). Once both barrels are reamed, then they should be cut and squared, to length. New barrels are then soft soldered in, the joint being large enough that silver brazing is not necessary.
I was of course referring to the "donor barrels "
As to the method of machining you suggest , let's say it is not the way I have sleeved many hundreds of guns during my working life .
