Marl3y, I have a different take on looking at this situation, but first, I need you to fill your gun tank to capacity and write down the pressure, then start taking shots without valve spring, hammer spring, Macro/micro and write down the tank pressure drop at each shot or group of shots until you get at least 20, or more to make it statistically significant; else, its a WAG. Report back the pellet weight, velocities and pressures, also the tank volume if it is a 300 cc, 400 cc, or 580 cc, and fill pressures either 250 Bar, or 310 Bar.
The best place to start is by setting your valve spring adjuster at the center, the macro at 8, and micro at 3. Then adjust your regulator for your desired velocity. Keep in mind that the best combination of precision accuracy AND power is right below 889 feet per second (fps). Once you go above that you will have more power, but at a loss of precision due to entering transonic turbulent Eddie currents that play havoc on projectiles from spit wads to 747s. The 889 fps is at just below Mach 0.8 at STP, and you don't want to hit that wall. The Mach is taken at station and varies with the speed of sound which is approximately 20 x sqrt (absolute temperature), so each degree Fahrenheit will change the speed of sound by about 1 fps proportionately with temperature, as a quick and dirty rule of thumb.
Now, the reason I need said numbers and values is to calculate the air mass in the tank, plenum, and thus the amount of air per shot and how many fpe per grain of air you get. For instance, every website I've visited that puts out the specifications on the FX Impulse in 22 caliber shows that the 22 outperforms the other calibers by around 200%, which is ridiculous. I did some simple ratios and proportions then it did not seem right so I did some statistical mechanic formulas and it appears that the FX Impulse M3 is very close to the proverbial perpetual motion machine; in other words, impossible, and not just improbable.
Once I get your numbers and crunch them down to the individual grain of air at 1 atmosphere you will see that it only has so much energy, and in order to take advantage of it while being as efficient as possible, you must back down from the highest power peak, which means you want the valve open for no more than 7 inches of pellet barrel travel so you have the most efficient pressure at the muzzle as the pellet exits. If you get a few fps above, you will also have a much higher pressure which translates to wasted air for the small velocity increase.
In addition, shot count and power are on a teeter totter balanced by a fulcrum that is the compressed air pressure and volume in cc. You cannot increase power and shot count unless you raise the cc, or pressure, but better both, so set your goal and let the shot count fall where it may, of course you can have the most shot count with your goal velocity is you adjust everything in unison for the most efficiency at your goal velocity.
Lastly, I presume that you have a 580 cc bottle at 250 Bar (3,626 psig, or 3640.7 psia, which absolute pressure is needed for the calculations), which better would be a 300 Bar bottle, but I'll calculate with 250 Bar. Said bottle at said pressure contains approximately 2,660 grains of air at 70 degree Fahrenheit. If your regulator is set at 115 Bar, which is where I would start, The 115 Bar (1,668 psig) pressure is like a preload where every shot is at that energy level, and at that energy level preload has approximately 1,219 grains of air that will not be used as it is there to hold the preload pressure of 115 Bar; therefore, the difference of 250 - 115 = 135 bar (1,958 psig), which equates to 2,660 - 1,219 = 1,441 grains of AVAILABLE air for the shot count from full fill down to the regulator pressure. Now, I can predict how many shots you can get with an efficiently tuned gun that uses 4 grains per shot, but first I need the mass and velocity, or fpe of any of the shots in the string, so lets say your 18 grain pellet travels at the best combination of accuracy and power of 889 fps, which would give you approximately 31.58219265 fpe, if you were at sea level and at 45 degree latitude, else, you might be a millionth of a fpe off. Great so far, we'll round it to 31.6 fpe then we divide by 4 fpe per grain of air to get 7.9 grains of air per shot. Then we divide the 1,441 available grains of air by the 7.9 grains of air per shot, and we get 182.4050633, but we only recognize integer shots, so the shot count would be 182 shots as a prediction. With the numbers you provide, we can adjust the air usage. Remember, you only have 1,441 grains of air available, and not 1,442, which means there will be those that will claim that they can get more energy out of 1,441 grains of air at 70 degrees Fahrenheit, and those people I would have to agree with because that is how wars are started.
In conclusion, the laws of physics are not just really good ideas, and numbers do not lie, but you can lie with numbers. I almost ordered the 22 caliber FX Impact M3 with the 700 mm barrel because I loved what I seen, and I'm not talking about the rifle, but the numbers, but after crunching them, I think i am going with the 25 caliber, unless I get my prototype patented and book finished with entertaining-educational videos to follow.
Take care, stay safe and Godspeed.
FJB Out!