I had the same problem a few years ago with an Air Force rifle.... stuck check valve. Called Air Force and they told me to keep tapping lightly with a plastic mallet.... worked like a charm and have never had a problem with that rifle since. Jeff
Ed, it sounds like the check valve at the filler port on your gun is stuck. Try tapping the side of it a few times with a screwdriver handle, then put some air into it, tap it again, and bleed. See what happens.