I'd recoment taking a look at the RAP4 pistols as far as internals go because it would serve as a decent base for your project. Get one, tear it down and see how the parts work. That may help you on your current issue.
My goal is not complexity. Those pistols are built off the .43 platform and thats not what I want either. The valves are completely different in design and don't even operate in the same fashion.