Tuning Air Venturi Avenger Shot count tuning

So I have a Avenger and I only shoot target paper. I have set the reg to 1200 and HS all the way out to zero. using the crosman 14.3 walmart pellets

At that setting I get about 60 shots at about 806 ft/s ,extreme spread of 118ft/s ,standard deviation of 23ft/s and 19ft/lbs 

Is this normal cause other people seam to be getting a lot more shot at a higher reg and HS

I know I dont have a leak at the vaule nor air coming back from breach



Is there some where else I might look? am I expecting too much from this gun?