Twobobb,
What I have found to be of great help is that I keep a notebook on each gun I regulate, and I put down the caliber, the barrel length, the load, and the final spread at the middle spacer and the front spacer. I also diagram the barrels showing measurements between each of the components that make up the barrel set, including the diameters of the barrels at different points. Even though I use this to help me get started, no two barrel sets are the same, they all vary somewhat.
When I want to turn a set of barrels down, I know what has worked in the past and I have a starting point for doing the new set. I'm sure the large companies have something similar, though they don't have to go through all these details. They have large profiling lathes that can turn down two barrels to exactly the same contour and change any measurement they want just by programing the machine to cut a different profile. Bob