Weihrauch HW100 Advice Needed

when it gets to 50 bar, what happens? is it leaking? is it not allowing more air? 

if it is leaking air from the hole in the bottom of the frame, it has a bad O-ring on the Main Valve that seals the cylinder, 

if the cylinder will only take 50 bar, then it may have the O-ring in the fill port installed incorrectly or wrong size O-ring, or the gauge is bad.

what Gauge are you determining the gun Pressure from? 

the guns Gauge or the Compressor/ pump gauge?