If you are seriously embarking on tuning your airgun for best precision, optimum velocity, regulation pressure, and hammer tension, graph your shot strings out as fps vs shot number AND also keep track of what your cylinder pressure is every 3-4 shots. You’ll want that pressure data later to understand what your regulator is doing relative to your hammer spring energy “requests.”
If your gun already has a know best velocity and pellet combination. Use that velocity as your “optimum velocity” for which to tune. Otherwise, you must first find your own “optimum velocity”
1. Shoot multiple groupings at various velocities. Start with HST set to a low velocity. Shoot groups. Refill the gun and shoot the next set of group with velocity turned up 5 FPS. Repeat until you have a range of velocities tested for precision. The velocity that has the tightest groupings is your “optimum velocity”
I’m assuming you want precise delivery.
Now you know the most accurate velocity for your gun.
2. Fill your gun. Adjust hammer spring tension to achieve “most accurate” velocity determined by the prior step.
3. Shoot a shot string down to where regulation ends and maybe another 10 shots more. PLOT the shot velocity vs FPS curve. Also write down cylinder pressure every 3-4 shots. You can tell how the regulator is set relative to demands of the hammer spring by examining the right end of your graph. Basically…
The end of regulation on the graphs is where your regulator pressure is currently set.
Regulator pressure setting relative to hammer “request”…
a. Too high if the velocities climb UP at the end of regulation and then drop back down.
b. Just right if velocities remain nearly level even a few shots past when shots would climb up in velocity in condition a
c. Too low if velocities begin level, but begin to slope down or drop off early. No rise before the drop.
You will need to iteratively adjust the regulator until you achieve condition b while velocity in the regulated segment matches your optimal accuracy velocity.
Now if you have a regulator tester AND have good data regarding what is the best regulated pressure for your gun, you could just set the regulator to the usual best for your gun. Then do all the adjustments using the HST to match the regulator setting. You might not end up at the optimum velocity for YOUR gun, but it is a bit less work. That calibration tape -- I would consider being accurate as a similar tape next to your car's accelerator pedal to estimate speed. It is better than nothing, but only a regulator tester or shot string plot will get give the actual pressure setting.
Tuning takes a lot of patience and meticulous record keeping. Every time you adjust the regulator, you need to adjust HST to set velocity back to your optimal accuracy velocity. Shoot another string and look at the graph.
The above can also be done with the regulator set to a specific pressure and then velocities adjusted to match the regulator, but that would not put you at your previously determined optimal velocity. That requires a regulator tester and pre-knowledges of best settings from others experience. With a chronometer, you can find your own best settings. Without that you are basically lost and blind.
Everything interacts. You need patience, but overall tuning process will pay off with a gun set for consistent velocity across maximal shots that are also at your most accurate targeting.
