This is a big can of worms here so let me go through every component of this that I can think of off the top of my head in order (I'll try to, at any rate) of ease of fixing:
1. Paint size. You could very well be shooting paint that either starts out as or swells to be too big for your barrel. Solution to that is to either shoot smaller paint or get a larger bored barrel, or switch sizers on it if you have a Freak, OTP, CP pro, JT, or Dark Series.
2. Breach could be dirty and have something like a bit of sand or paint shell. Clean it out.
3. Ball detent could be too tightly screwed in or stuck. Take it out and clean it, screw it out a little bit, or get a new one.
4. Bolt face could have sharp edges or cracks that treat balls badly. Smooth it out or get a new one. (Ouch on price there.)
5. Operating pressure too high. Get a better flow valve and bolt, probably reg too. (Major ouchie price.)
6. Your paint just plain sucks. Get better quality paint or take better care of what you get.
For much more help than that, I'd have to know more about what your Cocker is doing, either by your description or, if it's more complicated than that, seeing it in person.