Have you considered honing the bore of yur barrels? Are they a throu bore? No deliberate taper?
A Sunnen cylindrical hone can give you a 2 microinch finish and true cylindricity of less than 0.0002" error. I've used many bore finishing methods over the years, reaming, boring, swaging (some call it "ballizing"), honing, etc. None beats reaming for quick stock removal and to an extent bore straightening. None beats honing for generating atraight round bore provided the hining unit used is of suitable length.
Swaging (ballizing) requires a certain minimum strock, a minimum wall to support endwise swaging force, a maximum of wall allowing for expansion (the metal has to go someplace), and a smooth enough bore that the swage can displace metal to fill the discrepancies. The Cogsdrill rotary swage displaces metal laterally into bore defects but while it will extend displacable metal endwise a trifle you have to have a near net size bore to start with. If sufficient metal isn't there it cannot be displaced to fill voids with neighboring high metal. All have limitations although when properly implemented, swaging does provide near perfecly finished and sized bores.
Reaming when properly implemented can produce superb bore sizes and finishes if the proper stock allowance, reamer prep, coolant, bore prep, feed speed etc are selected. Straight round sized bores? Certainly. Mirror smooth bores? Probably not. But all the variables have to be controlled and implemented. Screw up one and the quality of the work suffers.
Honing a paint ball gun barrel bore to very close tolerances to a mirror finish is very possible but the cost of implementation may be pricey - several hundred dollars and you have to start with a fairly good bore. A multiple length Sunnen honing unit, a feed unit you can mount on a spindle (no sense spending thousands on Sunnen honing machine), stones, a bucket, oil, and aquarium pump, etc. are all (whew!!) you need. Not really a recommendation but something to think about.
http://www.sunnen.com/graphics/assets/documents/ee16b4ec3e7f.pdf
Have you though about using hydraulic chrome-wall tubing for paint ball barrels?