My GS just did a Rem Sendero 7 Rem mag to 7 mm STW for me ! BUT he also did it properly resetting the barrel and cut a NEW chamber ! So many GS's just run a reamer in and bore it out leaving the shoulder ring around a fired case .
RJ
Your smith did do it properly. There is no other way I know of to keep the reamer under control. Setting back the barrel by at least the length of the tenon allows for way more control. That being said, your original chamber must have been cut true in the first place.
As for leaving a shoulder ring. That just means the smith did do his due diligence and figure out how deep he had to cut to completely clean up the original shoulder.
I recently opened up a 260 Rem chamber to 6.5x55 Swede. It was done on a heavy profile Remington take off barrel. It didn't shoot well from the factory, or at least not as well as the owner wanted.
He bought a new barrel blank etc, etc and didn't want the factory 260 barrel cluttering his stuff. I traded him a bottle of Appleton's for it.
The barrel started out at 26 inches. It's now 24 inches. I cut two inches from the tenon end so that I could clean up a chamber that was slightly offset. Not much but enough. It can happen, especially with factory chambered rifles. Remington doesn't use piloted reamers. They depend on their CNC set up to give them proper alignment and they don't screw up often. These chambers aren't worth bothering with, unless you're doing it yourself.
The barrel was cut back right to the shoulder then it was chucked up, at the chamber end and the bore was centered with a dial gauge on a bore pin at both ends. The muzzle end was centered in a spider attachment at the rear of the lathes spindle. Then the remaining old chamber was cut out with an inside diameter cutting boring bar. This allowed the pilot on my reamer to enter the bore and center, without any side resistance from the old chamber.
I cut the chamber first, about .020 short, then cut the threads while it was all set up. Screwed on the receiver to make sure the printing was properly indexed, cut back a few more thou off the shoulder to where it would index properly and took measurements from there. Ran the reamer in again with my floating reamer holder and checked in all in place again, before releasing the barrel from the spider and chuck.
This is the way I do it. Doesn't have to be this extreme if the original chamber is cut true in the first place. All of this takes TIME and for most smiths, time is their bread and butter. This is why some smiths will just tell you to get a new barrel. The time cost can be more than the cost of a new barrel.
Then there comes the fluting. Most smiths I know don't have the tooling to cut straight flutes in barrels and that tooling, which is seldom used, is darned expensive. That means he would have to job it out to a sub contractor and charge for shipping both ways as well as the contractor plus profit price.
I made up an indexing barrel holder for my milling machine and used it for "one" job. It requires a constant flow of cutting fluid to keep things cool and for most mills such as mine, which is a manual machine, extreme care must be taken to make sure alignment to the axis of the bore is perfect, Again, this is done with bore pins and a shaft stub in the spindle taper device to measure the distance from the outside of the stub (Broken off shank from a 5/8" endmill bit). This has to be done horizontally as well as vertically to both ends and it doesn't happen in a few minutes.
There is at least an hour or more into the set up alone.
If this job were a frequent occurrence, then it would be prudent to set up special jigs. It's not and it isn't a job I relish doing. If the flutes are cut to fast the process will induce heat stress and maybe warping.
If everything isn't perfectly aligned the end result can be noticeably fugly