Classic: help gun's leaking

[k9hero]

I own a Classic with a nitrogen tank that is hooked up into a pmi co2 chamber. I had a Regulator on the gun but people at this Forum told me that it was the culprit of "shoot down". Now the gun leaks out of the back where you adjust the velocity. i have adjusted the velocity and it would still leak. i checked to see if any o-rings where broken but there all fine.
The Tank itself is a PMI 48 CU, 3000psi,

Please help, my first automag

[speedyejl]

Replace the reg seat, and make sure you put it in on the side that snaps in. Also once you do this dont open up your reg/valve after unless it leaks again, other wise you will need to replace it everytime.

[xen_100]

another thing it might be is the overpressure valve in the reg piston.

[Shirow]

Are you using an expansion chamber? If so, get rid of it. It won't be the cause of your leak, but running hpa through an expansion chamber is, at best, pointless.