Barrel manufacturing is a kind of "black art" we don't hear much about anymore.
Back in the day, an ad might have bragged that their barrels were "gun drilled" or "micro honed", but you don't see that much anymore- today's trend is to just tell you the bore size.
Now, to start with, virtually no manufacturer drills from solid bar stock these days. Most manufacturers buy special-order extruded tubing; special order to get a specific bore size- most off-the-shelf pipe or mechanical tubing isn't the right ID or
OD for a paintball gun barrel.
That tubing is often only minimally finished- in the case of, say, Pro-Lite, Carbine and A5 barrels, the only "finishing" was a couple passes of a relatively rough hone (I'm guessing 400 grit) and threading. I'm not sure they were even turned externally.
From the look of older (early-mid 2000s) Autocockers, their barrels weren't even honed. Whatever size the extruder produced, was the finished bore size.
Now, while I don't know for sure, I suspect that most manufacturers do something like roller burnishing. For example, they get raw, extruded tubing in, say, .682" (just throwing numbers out) or so, cut it to length, and then pull or push a roller burnisher
The burnisher essentially just rolls the surface smooth, like using a rolling pin on cookie dough. That "squashes" the metal, resulting in a .683" or .684" (or whatever) finished bore.
The rolled blanks are then fed into whatever CNC lathe does the threading and external profiling. (Though with the right setup, a bar-fed machine could burnish, profile and part off- we're just concerned with bore finishing at the moment.)
The burnisher is faster than honing (essentially one pass vs. multiple passes) doesn't wear nearly as fast as abrasives, and produces a much smoother finish.
Making a stainless
barrel however, would be different- stainless, to my understanding, can't be roller burnished because it work-hardens. Those barrels would have to be bored and likely honed and polished.