Something many players don't realize is that different brands of paintballs are different sizes. If your paintballs are smaller than your barrel, it doesn't matter how consistently you deliver air, each time a different amount will escape around the paintball and you won't be able to reliably shoot your paintballs. To find out if your paint to barrel match is good, remove your barrel and place a paintball into the back of it. If the paintball freely rolls down the barrel, the paintball is too small for your barrel. If the paintball sticks in the end of the barrel and doesn't move, then blow into the barrel with a normal puff of air from your lungs. If the paintball is blown out with one breath, it's just the right fit. If a normal breath doesn't budge the paint or only moves it partway down the barrel, the paintball is too big.
There are two ways to get a perfect paint to barrel match: find the brand that fits your barrel (Compare Prices) or else buy a barrel kit (Compare Prices). There are dozens of different brands of paintballs available online, at pro shops and at many sports stores, so you should be able to find a brand that fits your barrel. If you don't want to be stuck with just one kind of paintball, a barrel kit will let you adjust your barrel size to fit your paintballs. Barrel kits come with either different sized inserts or else separate sized barrels so that no matter what kind of paint you buy, you'll have a perfect match.