With a pellet or dry fire? Ill use more air per shot when there is no pellet (with a pellet, thee is some back pressure that conserves some air per shot).
Does sound about right to me, but youll need to test to see how many of those 30shots are useful to you. With a stock Discovery, would expect about 20 -24 of those shots to be pretty tight in velocity. Even at closer (30yards or under) range, once the vel. starts to drop, the pellet does strike low.
With a chronograph, most of us shoot long strings of shots to find out where the most consistent shots are. But even without a chronograph, can still figure out when the time to stop is.
Set up a target at your normal range (Id suggest 20 to 30 yards as a minimum). Fill gun and start shooting at the same target. Once you start seeing pellets landing a bit low, know that youve run out of good shots.
Shooting moldy dry wall, this time at 32 yards, but even without a chronograph, can tell that something just aint right with the right handed group. Both groups are from a .22 Discovery, but on the right hand side had it cranked up as high as possible (939fps/14.3gr.). By shot #3, impact was seriously was dropping.
Group on the left is the same discovery, set to 805 fps. Could easily have gone another 10-12 shots with the same point of impact.