1. Fill the gun. Take ten shots at an aim point and make these shots 20 seconds apart.
2. Fire ten blank shots.
3. Fire ten shots at a new aim point at 20 second intervals.
4. Repeat stages 2 and 3 twice.
5. You now have four cards to compare. Compare the strike points with the aim points. Has the centre of gravity shifted, from group to group?
Now fill the gun back up to the original pressure and repeat stage 1. Has the strike point gone back to the original place?
If the answer to these questions is yes then you may have the problem that some early EV2s had. It requires a trip to the factory and the regulator housing binned and exchanged for a new one. It's all to do with screw threads cut on the wonk so to speak, and the cylinder moving with changes in internal pressure. With the muzzle fixed to the front of the cylinder, it pulls it off line.