The paint should fit into the barrel and just barely touch on two sides. That is the ideal paint to barrel match. If the barrel is not removable, then there isn't much you can do about it other than finding a type of paint that works well for you.
If the accuracy is bad, turning down the velocity can help. Start low and increase the velocity towards 300fps until you see a decrease in consistency.
A lower velocity can also increase your efficiency and shots per CO2-12gram.
Except for the Automag in front, its usually the man behind the equipment that counts.