Re: Chambering goals
Old Harry Pope did just that. He would drill, bore, lap a barrel out, CHAMBER IT, fit an insert into the chamber, and then rifle the bore..... Not many people have the TIME to have that done and I don't know if the riflers would think about it. Of course a few guys are doing re-boring of barrels and that would be similar, but you go from say a 30-05 to 338-06 you will still be running a neck and throater into the chamber to complete.
But really, is it worth the effort? I don't think so, at the time Harry did, but he did all his own work and it probably didn't add too much time to change the sequence some. I believe the chambering reamers we're using today probably work a tad better than those of the past also.
I know a few guys at a cut-rifle barrel shop, at one time I did think about just getting a drilled and reamed tube from them for me to fit and chamber, and then have it rifled afterwards, but with the methods most use now for set-up before chambering would be no different, and lapping out a barrel after rifling may wash out that 'perfect' throat you were hoping to have.