Yes. Any of the major barrel makers or custom gunsmiths. MOA
It MAY. There are multiple factors that affect accuracy. The stiffness of the barrel is ONE of them, because a thinner barrel will heat up faster. When a barrel becomes very hot from fairly rapid fire, the accuracy begins to suffer.
These are two separate questions, but yes, barrel lenght and propellant affect the distance and accuracy of paintballs.
The barrel is long enough. Accuracy- depends on your definition of accuracy, and extreme ranges. To me, that is in excess of 1000 meters, and I would not be using a rifle with a light sporter barrel for that, no matter what caliber.
30 inches. A longer barrel gives you better accuracy.
No
The barrel has deep grooves milled into the outside of the barrel. Called flutes, the grooves reduce the weight of the barrel, yet leave it a stiff barrel with very good accuracy.
No. Since you will not be able to apply a consistent coat all the way around, trying to lubricate the inside of your barrel will greatly decrease accuracy.
Use a density factor to make a barrel to ton conversion. The ton is a metric weight and the barrel is a volume measurement.
NOPE. with out rifling, be it barrel or slug itself, there would be no spin on the slug. You would have minimal accuracy.
It may or may not depending on the ammunition used.
It may or may not depending on the projectile and velocity.
The rifling is there to spin the bullet, which gives greater accuracy.