Was the barrel used or new. Look down the inside and see if there are any large scratches or rough spots. And you can try rolling the barrle on a flat table to see if its curved at all.
For accuracy's sake (as well as consistancy) it is usually a bad idea to mix different types, batches, bags, ect of paint. Check them over to see if they are in good shape. are they round, do they have dimples, has the paint settled (you can sometimes see a line that shouldent be there).
If it all looks gun try putting the a ball in the barrel. if the paint drops through the balls are to small. if you turn blue when you try and blow the ball out the balls are to big. If the ball fly's across the room you have a good fit and a mess on the wall.