If you have 150 Bar in your rifle tank and 150 Bar left in your carbon fiber tank, you could open the line up and never be able to put any air in your rifle tank because the pressure in each would be equal … 150 in rifle and 150 in tank. So ... no ... you cannot use every last PSI in the tank unless you would be satisfied with only filling the rifle to lower and lower pressures. Once the Wildcat gets below a certain psi level, you will not have enough air pressure to propel your pellet fast enough to stabilize the projectile in flight. In order to put pressure in your gun, the pressure in the tank must be higher than what is in the gun, otherwise, if they are equal they are static and no pressure goes anywhere.
If I understood what you were saying in your post, you said that you had the bottle filled up to 4000 psi and you only got 40 shots from the gun and the gun would not fill past 150 Bar and now your tank is down to 2000 psi … I can only speculate that your gages are wrong. The article says that the valve on the tank has 2 pressure gages, one for the tank on the gun and one for the air in the fill tank. What does the pressure gage on your rifle read? The other option is that you might have a leak on the tank because there is no way you could have filled the tank and only got 40 shots off and be down to 150 Bar now.
Get an empty plastic container with a spray valve on top, like a Windex bottle. put some dishwashing detergent in the bottle and fill with water. Spray the soapy water around the fittings on the bottle as well as where the fittings are connected to the bottle and see if any bubbles start coming up. If you do, that means you are losing air from the bottle and have a leak.
