Young feller, do whatever makes your insides warm and fuzzy. Your so called "machinist" friends need to go back to a basic machining class as Jackie said!
For starters I am not young and the gentleman in question has been a machinist for 30 +years and runs some high dollar equipment think 6 figures plus. The company he works for builds precision parts.
They do not let guys that don't know what they are doing run machines like that or build precision parts on them with million dollar contracts on the line.
You are assuming a lot that you can straighten that hole better than the barrel maker who made it who more than likely has better tools, gauges, and so on our you would be making your own barrels.
How do you know it is off in the first place? Sure all bores curve but you what looking at 3 to 5 inches or less in depth from when they started the hole to just about any throat out there.
You are going to tell me a high quality barrel maker in this day and age does not have that hole in that short of a distance dead nuts? Really?
Pre boring was designed for one reason so a gunsmith could save on reamer wear period.
If its the end all be all why is a guy like Robert Gradous not doing it?
Let me guess Robert does not know that a hole can be straightened right?
Like I said the theory is flawed you are assuming the bore is already off so you need to go in and line the chamber up to it.
If you are really convinced that hole is off why chase the hole than run a boring bar? Why not just start with the boring bar and skip the drill bit?
You are also assuming you are not getting any tool deflection because of light cuts but your cross feed does have any deflection or the boring bar or tool holder right?
I did not learn from a rifle builder I learned from a machinist and shooter who has done really well in the shooting world and guess what he does not pre bore either.
So you want to pre bore go for it. You want to chuck it up in a 4 jaw and just dial the throat in and never mind the wobble on the back half, Cut the threads and chamber knock yourself out.
But do not try and tell me its more accurate than dialing in the throat and breach in and then running a reamer in because the results I see and thousands others see doing it this way speak for itself.