I received a message from someone who had trouble understanding my explanation of how to set the regulator pressure and hammer spring tension on pcp rifles, so here is the explanation on how to do this from Huma. Hope this explanation answers any questions that mine did not…
Best regards, Chuck
How do I adjust my rifle properly:
There is unfortunately not one general answer to this questions, but we will try to help you out with some advice to understand the principle of a regulator and the settings. Please note, all information in this sheet is general, and just an indication and may vary per model and type of rifle.
The basic step:
Start to adjust your rifle so it shoots with a constant pellet speed. After the rifle is shoots constant, start working on the preferred pellet speed; changing one setting at the time Respect the common regulator pressure setting: These settings are based on average FAC rifles. .177 in 8,4 gn. is around 125 bar. .22 in 16 gn. is around 130-135 bar. .25 in 25 gn is 140-145 bar. (BSA rifles tent to be a bit higher) These pressures should bring you close to the average pellet speeds of about 270- 285 m/s. Adjustments can be possible but only if you know what you are doing. Short barrels need more pressure to speed up the pellet compared to longer barrels. Heavier pellets also need more pressure to achieve the same speed as lighter pellets.
Airflow:
Your rifle’s power is determined by a mix of components like hammer weight, hammer spring tension, regulator pressure and diameters of transfer ports and or other air restrictions. Most rifles use a sort of “self regulating behavior” of the valve. This is based on certain transfer port diameters combined with valve diameters. When using a regulator you do not need this “self regulating behavior” anymore and you will get the best results when you optimize the airflow. Remove restrictions (as far as they are used in your rifle) and check transfer port sizes. (Normally FAC rifles already have proper diameter transfer ports)
How to adjust my hammer spring tension in combination with the right regulator output pressure:
When you have fitted your regulator start using the lowest hammer spring tension and start shooting and measuring with a chrony. Shoot slowly like on the range. After every shot turn up the hammer spring tension a bit. You will see a small adjustment of hammer spring tension will give a relatively higher pellet speed. At a certain point you will notice although you can adjust the hammer spring tension even more, the pellet speed won’t get higher or even gets lower. This means you have reached the maximum pellet speed in this pressure setting. If you would like a higher pellet speed, please adjust the regulator pressure some higher, following the instructions here. 10 bar increasement will approximately give 10 m/s more pellet speed. Too much hammer spring tension with too low regulator pressure will resolve in high air consumption.
When you followed the steps above and you notice you can get a pellet speed much higher as preferred, you should also decrease the regulator output pressure. If you continue with a too high regulator pressure, and you adjust the pellet speed only with your hammer spring tension, there is a possibility your pellet speed will climb when pressure gets below the regulator set pressure. Hammer weight: An unregulated PCP rifle needs a relative heavy hammer to open up the air valve in the full pressure range (200-100 bar) When a regulator is fitted you will have a constant “lower” pressure on your air valve. This means the hammer can open the valve easier and often does not need as much power and weight compared to an unregulated rifle. Sometimes losing some hammer weight can have a positive effect on the air consumption. Please don’t start drilling and grinding on your hammer directly, but check the several airgun forums. You will find a lot of information on your specific rifle and tuning it to even higher performance. Whenever I find usefull video’s on the web I will post the links in the fitting instruction.
 
