Aftermarket barrels. A longer barrel will get your paint into a smaller spread. Try Stiffi, Smart Parts, or Dye barrels.
The answer is all of them
Fletching an arrow stabilizes it during flight and improves accuracy
Almost all barrels are made with a slight overbore. Too much overboring will cause the paintball to lack power.
Two piece barrels allow you to change the diameter of the bore, which lets you fit the paintball better, leading to more accuracy.
These are two separate questions, but yes, barrel lenght and propellant affect the distance and accuracy of paintballs.
No compressed air would be better for accuracy as well as your gun. Its like co2 but at a higher pressure with cleaner air and no liquid that can damage your paintball marker.
It depends on the grade of your paint, and how good your paintball marker is. Paintballs will almost never get ball on ball accuracy.
for each single shot markers themselves are not any more accurate than any other marker, the barrel can help with accuracy and shooting good paint is the easiest way to improve your accuracy. player skill is also a large determining factor, now if you are shooting a string of paint you are going to want a marker that has as little kick as possible so you can hold it as steady as possible, in which case look into a spool valve marker as they have the least kick out of any design
A shoulder stock permits a more steady aim, and generally improves 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.
For optimal performance with a paintball gun, it is recommended to use high-quality, tournament-grade paintballs. These paintballs are more consistent in size and shape, which helps improve accuracy and reliability when firing.
It improves that accuracy and distance of the bullet by causing the bullet to spin not tumble like a smooth bore barrel musket.