"What builders currently reliably produce the tightest concentricity to bore in the chambering process? Which ones have the best accuracy/precision in the field? "
-Every single one of us. Just ask us, we'll tell you.
This kind of question is really a bit silly. Personally, I don't care if a guy chambered a rifle with a Dewalt and if it has TIR with as big a number as anyone cares to stick in the conversation.
The bullet tells the truth.
If the rifle is producing the accuracy standard, then who really cares how, what, etc?
The truth is, the numbers folks like to quote are by and large fictional anyway. The inspection that I have seen everyone perform is always done with the barrel in the lathe. In ANY lathe you are going to have a tolerance stack. You are rotating on a set of bearings. Clearance has to be engineered into it for it to even work. Even a class 5 Tapered Gamut spindle bearing has clearance, which means there will be some runout. It's small, but its still there.
I have a lathe I paid north of $100,000 for in 2009. The spindle cartridge costs more than what a lot of guys paid for their entire machine. If we use that as a barometer, then I should be producing barrels with accuracy levels "X" better than brand "B".
I'm not. It would be a ridiculous statement to even try and claim that.
Let us really look at this for what it is:
1. Figure positional errors. The BEST cnc lathes repeat within a couple tenths (.0001's) and that is on a brand new machine. Get a few miles on it and stuff loosens up. If you think were all spending 5-6 thousand dollars on biannual PM's to check this stuff, were not. On a CNC, a lot of backlash error can be programmed out with parameter settings. On a manual, your going to have to resort to new parts once it gets bad.
2. Now factor in the clearance between the reamer and the pilot.
3. Now figure the TIR of the pilot itself.
4. Clearance between pilot and bore. It has to be able to move inside the hole. Barrels often have taper in them the first couple inches or so from lapping. So, what fits well at the saw cut on the breech end may very well sieze once you get down the hole a ways. That too must be considered prior to cramming the reamer in the bore.
5. Runout present in the barrel. They ALL do this. One out of a hundred might not as much. They don't shoot any better than the bananas do.
ALL of this adds to the value you are seeing on your $200 indicator. That is when taking a direct reading. Going the other way by stuffing some bushings and an arbor shaft down the hole only further aggravates the condition by a factor of "whateverth's of an inch."
To do this at the level where the answers become truthful, you need a well equipped metrology lab. That would mean a very large work envelope CMM. The kind that costs an absurd amount of money.
I once worked in a gear shop in Hudson, WI. I worked in the metrology lab. I programmed and ran a Zeiss/Hoffler CMM. It was a 1.5 million dollar machine. This was for creating what's a called a "K chart" on industrial transmission gears used by companies like Catepillar, Mack, etc for semi trucks. (one reason why they go north of 500,000 miles between overhauls.) These were on hobbed gears that are later ground, then polished.
I've yet to ever hear of anyone in the precision gun trade going to that level. It'd be pointless to do so as its literally cents on the dollar just to chamber it, shoot it, then decide whether its "good" or "bad". The ROI on a machine like that would take decades to capture.
Bottom line:
There is a long list of well vetted shops that frequent this forum. Chances are good that any of them is more than capable of delivering a barrel job that will meet the standard of what it takes to build an accurate rifle.
Hope this helps.
C.
