Cool, thanks for the reply. Yes, I know the "fins" dictate what size ball you use. Seeing as the fins are 2 inches long and the barrel is about 12-14 inches, I just wanted to keep my paintballs as close to the actual barrel size as I am presuming you would achieve the best results this way. Obviously, fin first, barrel second. I bought one of these Straightline barrels. It's in the mail, so I've yet to try it. I also bought the 2 extra fins(the 2 bigger sizes, which sounds like they will be closer to the actual bore of the barrel size) from hammerhead.