My local gunsmith told me airarm,s guns are set at 9.4 new dont know why, When i bought mine the shop chrono it at 9.4 they put it up to 11.6 as coney explained i had problem,s with it when it came back guess what.!!!!!! shooting at 9.4 again but my local shop changed it back to 11.6 i was lucky mine has,nt got the anti tamper screw on it. 
 
Mines does`nt have the anti tamper screw on it either GA at the gun shop tried opening the valve on the side no joy needs turned up internally mate. Like i say me mates gun was brand new s410 in .22 and it was doing 8 what a piss take . ATB FV