RA Tech will be offering soon their Custom WE PDW Super DX which is part of their custom work series. This is based on the open bolt system and they have improved the internal parts ranging from the inner barrel, hop up to the trigger housing unit, improved firing pin, bolt lock, hammer, and sear which are all CNC'd. Pricing will be US$495, shipping costs included, but might get higher depending on your location.

You check a comparison of their custom work against the stock WE Open Bolt PDW GBB by watching the video below: