How to Find the Magic Air Pressure

The other basic air gun is the adjustable power found mostly in 10 meter PCP .177 caliber pellet guns. Again, it receives its power by being filled from a tank like the Air Venturi 88 or a hand pump like the Hill Pump. Because the power needed to propel a lightweight .177 caliber pellet is minimal, all that is needed is consistent air pressure. To provide this constant flow, an internal regulator adjusted by the marksman lets just the right amount of air propel the pellet at the same speed over and over. It does not take a lot of pressure to send a pellet through a paper target; just the magic amount of air pressure usually under 12fpe.

Suppose that you are going to take a one hundred mile trip and your car gets ten miles per gallon of gasoline. Would you rather have a ten, fifteen or twenty-five gallon tank? If you choose a ten-gallon tank and there is a steep uphill grade that was unknown your engine would use more gasoline than estimated and you might have to walk the last few miles to your destination.

If you choose the fifteen gallon tank, you would indeed complete the trip but you would have to fill up before returning; and what if the price of gasoline was higher than at home? If you choose the twenty-five gallon tank, you would be able to go to and from your destination and still have gasoline to spare upon return.

Let’s say that the reservoir on a given fixed power air gun is filled to 3000 psi and we want to use a 7.8 grain pellet. After putting the gun into a gun vise we find that at the full power of 3000 psi the pellet travels at 737fps, with 9fpe and produces a 9mm group for six shots at 10 meters. No magic pellet here.

Now lets fill the reservoir on a given adjustable power air gun to 3000 psi and use the same 7.8 grain pellet. We lock the gun into a gun vise and start with the internal regulator all the way open. Same fps, same fpe and same 9mm group. No magic pellet here- yet. Then we turn the internal regulator down and begin shooting again with a new target. At a lower air pressure we see the fps and fpe go down, but we also see the groups begin to get smaller. As the internal regulator is turned down further and to yet a lower pressure, we see the pellet beginning to go through the same hole over and over. Just to be sure, we go a little past and the groups began to become larger again, so we increase the pressure using the internal regulator until we are back to repeating the same hole again. Now we have the magic air pressure which produces the magic pellet.

Hypothetically, lets say that the magic operating pressure is 1500psi and that the reservoir of the gun is now at 2800psi because air has been used to perform this test. This means that we can continue to shoot shot after shot until the gun reservoir drops below 1500psi. then it is time to refill the gun’s reservoir because we are now out of useful power.