Author Topic: Regulated gun tuned on the down-slope  (Read 68 times)

mcoulter

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Regulated gun tuned on the down-slope
« on: February 12, 2020, 05:31:11 PM »
Hello Bob,

Am I correct in my thoughts that having a gun showing a shot string similar to your down-slope example in the link below, that my two options are to either increase HS tension or decrease regulator pressure?  (With the goal being to try to eliminate the slow rise in velocity and then the surge at the end of the string.)

https://hardairmagazine.com/ham-columns/tuning-regulated-pcp-airguns/

Background - I picked up this used Cricket .25 that came with a 4.5 cm plenum extension and a rather fancy hammer spring adjuster that also included an extra weight that sat behind the hammer.  This adjuster was causing some extreme binding and I was able to replace it with one that was more traditional and did not include the weight.  I suspect that the actual hammer spring is probably standard, but I don't know about the valve spring.  The regulator is a huma and came to me adjusted to 120 bar. 

Here is a recent string:

https://photos.app.goo.gl/7QWLs7CCSj5WjRkVA



I also suspect that I'm still not getting a consistent hammer hit.  I have noticed that the plating on my replacement adjuster is starting to peel off and may be causing some of these smaller fluctuations from shot-to-shot.

Oh, here are some pics of the original hammer and the extra weight.  The weight looks like a nail and the "head" fits inside the back side of the hammer.  It is actually really well made but with my current spring, it binds badly.  Is I'm writing this, I'm wondering if it may be worth trying a shorter spring with that adjuster.







Any suggestions would be most appreciated  :-)

« Last Edit: February 12, 2020, 05:42:07 PM by mcoulter »


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rsterne

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Re: Regulated gun tuned on the down-slope
« Reply #1 on: February 12, 2020, 09:17:38 PM »
You are correct in your assessment.... If you want more power, increase the hammer strike.... If you want the same or less, reduce the setpoint pressure and then retune....

The large shot-to-shot variation while above the setpoint is typical of a downslope tune.... as the valve is operating in partial valve lock.... If you tune closer to the knee, that should decrease....

Bob
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mcoulter

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Re: Regulated gun tuned on the down-slope
« Reply #2 on: February 13, 2020, 01:05:15 PM »
Great, thank you Bob  :-)
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