There are a few simple routes you can go to prevent rollouts.
-The tape/nail polish method is where you take either a piece of tape or dot of nail polish and stick it in the inside of the barrel, just in front of the bolt, in front of where the ball sits. This leaves a little bump, restricting the bore just a bit keeping the paintball in place. It essentially acts in the same way as an autococker detent.
-You can also send your gun to palmers where you can get "wedgits" installed. This is where they take a punch, and do essentially the same thing as the nail polish mod, but they actually punch the barrel itself so that it deforms into a little bump
-A more complicated option is to rebarrel your gun yourself or send it in to someone to rebarrel it in a smaller bore. The member "tymcneer" on here sells small bore brass tubing for projects such as this.
These can all help with consistency because it will stop any partial rollouts you might get, though the rebarreling option will net you the best efficiency.