I thought it wise to put a short guide together to help those who at times wants to fiddle a bit with their air rifles and are not sure where to start.
How to Balance the Functions of the Regulator Pressure and the Hammer Spring Pressure.
In PCP air rifles fitted with regulators it is important to balance the regulator pressure and the potential energy with which the hammer spring opens the valve. The objective is to get as closes as possible to a very consistent metered compressed air “pulse” every time that the hammer strikes the valve.
When this balance is not correct it will result in a poor shot count (over airing) and higher variance of the pellet speeds. (Extreme spread)
Over airing takes place when there is too much pressured air in the pre chamber area and the open valve is venting this air out through the open barrel. (At this stage the pellet has already left the barrel)
See Note 1.
How to determine if over airing occurs:
First step is to do a shot count with a full bottle and record speed and extreme spreads over 10 shot batches. Note all the settings of the hammer spring cap and the regulator.
Marginally back off the hammer spring pressure. Start with a 1/6 of a turn of the cap screw and continue until a decrease in the pellet speed occurs. If the speed decrease almost immediately then the pressured air at the valve area is fully exhausted and the regulator is not able to re-pressure the pre chamber while the valve is still in the process of closing. A near ideal set up.
If the speed does not decrease when the spring pressure is decreased by 2 or 3 turns of the cap screw behind the hammer spring then the valve is open for too long and results in wasting air.
To reduce the time that the valve stays open increase the regulator pressure or decrease the hammer spring pressure.
Adjusting the Regulator Pressure
Marginally increase the regulator pressure for the same hammer spring pressure until the pellet speed starts to decrease. At this point decrease the regulator pressure fractionally again to ensure that temperature differences will not cause a change in the pellet speed.
Adjusting the Hammer Spring Pressure
Decreasing the hammer spring pressure dramatically will result in longer travel time for the hammer. If this decrease in hammer spring pressure is causing the extreme spread to increase then adjusting the regulator pressure is preferred.
Do a couple of 10 shot batches and see if the extreme spread is acceptable. If it is not acceptable then in small increments:
Increase the hammer spring pressure and increase the regulator pressure to maintain the pellet speed until an acceptable extreme spread is achieved.
Decrease the hammer spring pressure and decrease the regulator pressure to maintain the pellet speed until an acceptable extreme spread is achieved.
This process requires lots of patience, pellets and time to do the tests.
It is assumed that the rifle is set up for a typical 800 feet per second and 12 to 20 foot pound energy. The mechanics of the air rifle may differ but the results will be the same. There are generally two extremes of rifles as per these examples:
- Theoben Rapid and TM1000 . A larger hammer, typically 68 grams in weight, is propelled by an elastic coil spring over a longer distance of about 15 mm before it connects with the valve stem.
- Walther LG300 in the 12 foot pound energy class. The smaller hammer, typically 35 grams or less, is propelled by a very stiff coil spring over a shorter distance of about 3 or 4 mm before it connects with the valve stem.