Don't run a regulator on an Automag; it can starve the valve. The valve is a regulator and is all you need.
Automags are not air efficient
I had a chipped sear recently which gave these exact results. Very frustrating to diagnose because it's typically not the first place you'd look. Take
I found the same thing in my reading on Mac brown, the oring was out of order.
That's the way I got the gun.