Sorry, I haven't got my regulator handy. It's at the shop.
I did find their user's manual online though:
http://www.madbullairsoft.com/doc/XC...r%20Manual.pdf
My guess is that you're going to have to disassemble the regulator to clear out whatever may be jamming the piston "Pressure adjustment valve" #13. I don't think removing the gauge will be necessary. It's tapped into a hole that's drilled to connect to the regulated side. You'll probably have to take out #14 though. I can't remember if that requires a pin spanner though.