When I wanted to build on a wildcat (26wssm Imp), I didn't ask machinists what to do.
I measured my brass, ran numbers in Quickload, filled out reamer prints and ordered what I wanted. The reamer maker (Dave Kiff @ Pacific Tool) made the set to my prints. That's what he does very well.
He's not me, building a gun, shooting and reloading it with my plan. All that's on me.
When I fire-formed my brass in my new chamber, I created my cartridge. I validated QuickLoad and reloaded per my plan. All worked out perfect.
Reamer makers are just good machinists, same as action makers, die makers, and barrel finishers. I used 4 separate machinists to finish my system, and each did their part -per the customer. They provided no inputs nor held influence about whatever I was doing.
After all, how much would they really know about what I'm doing?
My guess: about as much as Leupold or Berger, whom I did not pester to recommend a scope or bullet.
I will suggest that each specialist in the gun building endeavor is useful in their area.
Reamer makers can help you with choosing throat length & leade angle for the bullet you chose(it all begins with a bullet). A die maker may have particular experience about sizing for certain attributes of YOUR chamber & cartridge. An action maker might point out a better model for reliable function, with possible tweaks to port length or something.
Would I go with a reamer maker's ideas about sizing, or a die makers? Personally, I would go with the die maker, or neither. And for my build, that's kind of the way it went..
I sent a brand new shiny sizing reamer along with my fired brass, and body die blank, and reamer prints. I had suspected that my die maker might hold common notions of sizing that I do not agree with. That he would go too far (for my own good). So to stay on my sizing plan, I sent the die maker over-expanded cases(without his knowledge). That is, cases that were taken to pressures well over SAAMI max, and my intended use.
The die maker did do his own thing,, my sizing reamer was not used, and I got what I wanted. Perfect!
My seating die blank(Wilson) was cut using my chamber reamers(rough/finish). The barrel finisher did that.
Anyway, as mentioned I had measured my new brass and for a grand experiment I set my chamber as 'fitted'.
This is no more than 1thou over any new brass dimension, and why I know today how much brass springs back.
It's not 4thou, or 2thou,, it's less than that. And as far as brass growth, you set that with your chamber clearances, breach support, and load pressures. These I had accounted for up front (a plan), before ordering anything.
I only tell you this so that you can know the potentials here.
My 26wssm Imp. has the same H20 capacity as a 260AI. IMO, it is the best overall capacity for 140gr 26cal bullets.
My mid-node with a 28" barrel is 3025fps, 140VLDs, 47.4gr IMR4350, right at SAAMI max (65Kpsi) per QuickLoad.
I had worked up all the way to 3380fps, finding another node near there, but not as accurate. That's where I produced over expanded brass for my die maker. I'm sure his plan would have worked for that, but it was never my intent to run that hot.
I've gone through 2 1/2 barrels at mid-node and ~80 reload cycles using the same 50 wssm cases -with ZERO body or neck sizing.
Since I only went with 35deg shoulders, I do have to bump them(began at 9th reload). That's where my die maker trick came in, and what my sizing reamer would have done; to allow bumping without body sizing.
Next reamer, I'll go 45deg shoulders, or maybe even 60deg(haven't decided), and see if I can remove bumping forever.
From my perspective, you do not have to move brass ~4thou up & down with reloading.
I KNOW YOU DON'T
If you want to, that's your plan, then fine. But, you don't have to.