This topic hasn't got much action. Is it because everyone does it like Grit or is it because not many even index the bores?
I never heard of it. I subscribed to the thread in the hopes of a discussion on the condition/issue.
"If you love wealth more than liberty, the tranquility of servitude better than the animating contest of freedom, depart from us in peace. We ask not your counsel nor your arms. Crouch down and lick the hand that feeds you. May your chains rest lightly upon you and may posterity forget that you were our countrymen."-- Samuel Adams
Your question is simple but the answer is much more complicated than "who does what"
"How do you find the curvature?" you look down the barrel either in or out of the lathe.
Your eye needs to be a little trained to do this.
Don't expect to either see a curve, or have a curve that only goes in one direction for the length of the barrel. Every manf. seems to have a different handle on how to create a straight bore, and I'm sure some don't care. I typically use the barrel makers who try and drill nice straight holes.
Now depending on how the smith sets-up, and chambers, the barrrel will determine how effective or needed it is to indicate the curve. Or weather in the end it makes any or no difference at all.
If you ream start to finish with the reamer you may chose one way, if you drill and bore before reaming you may do it the other. Their is a multitude of ways to indicate and cut a chamber. I happen to think my way is the best, thats why I do it that way. Ask any smith and thats likly what he will tell you.
In the end no matter which way it was done, if it was done properly the difference in the guns ability to shoot will likly be more effected by other things in the process of the assembly, components and implementation.
Every (considered straight bore or line) is curved if the tolerance of measurement is fine (close enough). Gaging in thousands is like a potholed road compared to millionths..... or.... 0.001 versus 0.000001.... and it has everything to do accuracy of the machine tool, tooling, ambient temperature at which the machining took place, remperature at the cutting edge, operator skill and a multitude of other varibles.
In reality, nothing is straight, everything has curvature to some degree when the unit of toerance become acute.
So, the term straight without curvature applies to the degree of acceptable accuracy in the machining process, the cost of the process and the degree of acceptance by the end user in relationship to the cost......