Why can't you request the barrels come to you without chambers? You then will need to order your chamber reamer and gauges, and order the correct tooling you can chamber in the vise, with the correct tooling I can highly recommend this method if you are willing to take the time and proper care to do the job right. You will need to have the barrels in hand to order the correct bushing, you can send the bullets of choice to the reamer maker so they can get the throat right also.

Select your brass ahead and send a sample along with the bullets you plan to use to your reamer maker to make the proper head space gauge for you also.

Hint, get the brass that easiest to find and lay in a hundred, if your are going to black powder your loads, you can order a custom resize reamer to match, die body blank. Going this way you will have a life time of shooting from your hundred, if kept properly clean.