Tuning Shot String Evaluation

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SpiralGroove

SpiralGroove

Member
Oct 20, 2020
1,675
2,038
Washington, United States
Hey Guys,

Just shot a (48) string from my HM1000x (.22 cal. - 18.13 JSB's) from 230 to about 200 bar. The first clip averaged 884 fps, second 893 fps, next 899 fps, followed by 906 fps.

My regulator is set about 127 bar and I'm using my low powered SSG with the HS nut almost touching my stock.



What can be inferred by the steady upward progression of the 48 shot string?

- Too much hammer?

- inconsistent regulator?

- Valve seat issue?

- Set-Point vs. Hammer (balance) issue?

- You Fill in your Theory ............................. 👍



Any wisdom is appreciated as I hate to rely on MY conspiracy theories😵.
 
Tune your hammer spring to be 5% lower than the max velocity the current reg setting can do. If that velocity is not pleasing to you, readjust the reg setting and start over again. Tuning this way can overcome small reg creep issues, which is normal with regs that have sat for a while. If the creep is severe, rebuild the reg with new O-rings, or whatever is needed.

Also, tuning this way will reward you with more shots within a tight ES beyond the reg set point.
 
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Kirk, if it’s not adjusted to the knee as Keith described, what you are seeing is a characteristic of the regulator’s input regulation. Its output pressure is highest when the input pressure is highest, and it declines as the reservoir is depleted. So my guess is the rifle is operating somewhere too far down the velocity curve. Meaning at the beginning of the string, the plenum pressure is a bit higher and the hammer doesn’t knock open the valve as forcefully (partial valve lock), and as a result the velocity is somewhat less. Later in the string, the plenum pressure is gradually declining so the hammer can knock open the valve better and the velocity gradually rises.
 
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