I have shot proto paint though my 06,07 and 08 and we have used it to test the markers at work in the past so am surprised that you are having a problem with that paint its usually quite good. If it chops in the barrel then i would say that the problem lies in your barrel or both of your barrels. If i remember correctly the proto paint is quite big so that could be the problem. Have you tryed different bore size backs when shooting this paint? Do you test the paint is a good match to the barrel before you use this paint? Are the barrels clean? Is it just with this paint? Lots of things to try if you have no luck then you could send the markers to Planet and we can check them over for you. Dont think the problem lies with the markers though. Sorry i cannot be more helpful but kind of hard to diagnose a problem without the marker in front of me to try differant things.