Hi. The usual advice is to believe the pump/cylinder gauge, but I've come across as many duff cylinder gauges as gun gauges. My suggestion is that until you can check, believe the gauge that reads high, as that way you run less risk of damaging anything - including you
. Next is to try your gun gauge on as many cylinders/pumps as you can and with a little bit of luck you will find out which gauge to believe. If all else fails, keep believing the high gauge.
Did you let the gun cool down? I don't know about pumps, but if you are filling from a cylinder it can take couple of minutes for the air to cool and the gauge to settle. Also I'd never fill my S400 past 175, as its muzzle velocity doesn't become consistent until then, and that gives you a bit of leeway.