A bit about PCP basics: PCP Air Rifles have high pressure air reservoirs. When firing the rifle, a hammer or striker will knock on a valve which will open a little and a certain quantity of air escapes. This release of air is what drives the pellet down the barrel. 

 

In an unregulated air gun you normally start with a pressure of about 200 bar. But after every shot this pressure will decrease. With the rifle at full pressure the valve will only move and open a small amount causing the rifle to have a lower muzzle energy initially until after a few shots the primary pressure is reduced and there is far less pressure pushing against the valve The hammer will still strike the valve with the same force causing the valve to open up more, giving your pellet a higher speed from the increase in air being released. Therefore you can see your point of impact (POI) “climbing” after a few shots. Then after a certain amount of shots the pressure begins to drop even further and your POI will start to decline as the muzzle energy drops. 

 

A regulator is a kind of internal pressure regulator that divides your pressure tube in two sections. The first larger section of the air reservoir will contain the “primary” high filling pressure. The second section is just a tiny pressure chamber (plenum) that contains a certain quantity of air with a pre-set pressure that is needed for the pellet speed you desire. This we call the regulated pressure. The regulator will keep this pressure constant every shot, until the primary pressure is equal or lower to the set pressure of the regulator. This will result in a very constant pellet speed, and also a steady POI of your pellet. Another benefit of using a regulator in your PCP air rifle is that your rifle will be set up to work in a relatively large pressure range. After fitting a regulator you can optimize your rifle to function with a lower, much more constant working pressure. This means that you probably won’t need as much hammer spring tension as before. This can also reduce air consumption. Sometimes the hammer weight can be reduced too, this will give less movement inside the rifle. This will optimize the shooting behavior of your rifle.