I don't know where your located but perhaps your gun is one tamed down for some markets like mine, Canada where the legal limit
is 500fps. Like I said ,my .22cal HW45 gets anywhere from 410-467fps, my HW75 .177cal only gets up to 360fps.
Try a lighter pellet for more muzzle velocity?
I wouldn't consider at your guns performance, that it would be defective in any way?