What are the contributing Factors Affecting ES using a SSG in a Regulated PCP?

[SpiralGroove]

Hey Guys trying to reduce the ES of my SSG to a reasonably good number (say under 10 over 50 shots) on a regulated gun.  I get roughly 160 shots per fill at 915 fps (480cc) using 18.13 JSB's and could only to DREAM to have it over the entire 160 shots - but is that even possible?

1) I know ES can be reduced by Pellet sorting.
2) ES can be reduced using a non-metallic striker (Peek/Delrin).
3) ES is reduced by eliminating excess friction (variation) between SSG components.
4) Shooting at specific pressure ranges on a unregulated gun.

Do SSG's with only one spring generate lower ESS's?
Do SSG's using lighter components have lower spreads?

What other factors have I missed?

Kirk

[Hack21]

Tuning for 3-5% below plateau velocity as Bob has recommended. Ensuring that there isn't sear drag would be another point. Avoiding non-dry lubricants in the hammer system. If the valve has very low lift, then a lighter hammer should help with ES in theory.

[nervoustrigger]

#4 is related but to call it out specifically, the regulator’s linearity can play into it.  Input regulation...how much the regulator’s setpoint varies when the reservoir is full versus when the reservoir has fallen to something just above the setpoint.

And temperature affects all sorts of things in subtle ways.  While it’s not generally going to be a big factor inside of a chronograph session, it’s certainly one that can render the chronograph data invalid when you find yourself shooting under different conditions.

Anything that affects lift and dwell.  For example, going with a really light valve spring (or no spring) will affect the pressure range over which the valve will self-regulate.  This is a characteristic that can be seen in a conventional unregulated PCP, and of course anything that helps produce a broader bell curve will make a regulated gun more agnostic of inevitable pressure variations.

Just a few things that can be added to the list.   

[Motorhead]

You can still have in imbalance in regulators set point to hammer strike energy being off either end of the bell curve.
Just like a conventional hammer spring if your balance is off so will be ability to maintain a tight ES

[SpiralGroove]

You can still have in imbalance in regulators set point to hammer strike energy being off either end of the bell curve. Just like a conventional hammer spring if your balance is off so will be ability to maintain a tight ES

Hey Motorhead,
Using a conventional HM1000x Hammer, what range of regulator set-points would seem more balanced?
Likely higher than my 117 bar set-point ... more like 130+ bar.

[Motorhead]

Would have too run the gun with test gauges attached monitoring a progressive filling and seeing where the bell curve naturally peaks with differing HST.
This generally done with the regulator put into bypass mode while you sort out what pressure and HST gets you on the peak of bell curve at the speed wanted.
That known you then set the regulator to that pressure, back off HST just a tad and your perfectly tuned just shy of the peak.

[SpiralGroove]

Would have too run the gun with test gauges attached monitoring a progressive filling and seeing where the bell curve naturally peaks with differing HST.
This generally done with the regulator put into bypass mode while you sort out what pressure and HST gets you on the peak of bell curve at the speed wanted.
That known you then set the regulator to that pressure, back off HST just a tad and your perfectly tuned just shy of the peak.

Yeah, I remember seeing a post you did back a few years explaining this process ...  darned if I can find it

[Motorhead]

https://www.gatewaytoairguns.org/GTA/index.php?topic=161376.msg155797217#msg155797217
there ya go ... 

[SpiralGroove]

https://www.gatewaytoairguns.org/GTA/index.php?topic=161376.msg155797217#msg155797217
there ya go ... 

Haven't re-read your post yet, but I just shot a 48 shot string from 240 to 200 bar with 18.13 JSB's and got an average velocity of 916 fps.  The ES was 28, but if you knocked off 3 shots, it was 23 or 2.51%.  All 3 shots were in the first 14 shots.  I think overfilling doesn't help ES.

You know, for unsorted pellets that likely pretty good.  I started to sort a them by whole number grain pellets (my scale doesn't show decimal points ) and realized ... I got bigger fish to fry  - not doing this

My first clip averaged 908 fps, the second 919, third 918 and forth 921.

[rsterne]

Tune too far below the knee (more than 5% below the plateau velocity) and your ES will tend to increase.... It is like an unregulated PCP shooting on the first half of the bell-curve, when the pressure is above the sweet spot.... The lowest ES will usually occur just below the plateau, but of course your efficiency will generally be less when tuned that way.... Like anything else, a compromise must be found....

It goes without saying that anything that causes an inconsistent hammer strike will hurt the ES.... However, small variations have a much more critical effect if the gun is tuned for the highest possible efficiency (ie on the downslope).... When tuned on or just below the plateau, quite large changes in hammer strike have little effect....

Bob

[nervoustrigger]

Kirk, regarding your comment about overfilling doesn’t help ES…
 
Earlier I mentioned the regulator’s input regulation characteristics.  That affects the state of tune as Bob just described.  At full fill pressure, the regulator’s output pressure is as high as it will ever be.  That has the potential to temporarily shift the state of tune further down the slope.  If it moves far enough down the slope, it would reach a state of valve lock.  However, long before you get there you will see symptoms of partial valve lock…and that’s the elevated ES we’re talking about.

[CableStop]

I would try using a different hammer first as that's easy.  Then maybe try a TSS or shorter spring.

Tune it until the initial performance is the same and see if the ES or shot count changes. Would at least help to narrow it down.  Sometimes diagnosing an issue is easiest by trial and error.

I know poppet material wasn't mentioned but PEEK poppets are very hard and since the material compresses less, it could give less variation shot to shot. It could also be made smaller reducing the required energy and allowing more flexibility with the SSG and hammer set up.

[SpiralGroove]

https://www.gatewaytoairguns.org/GTA/index.php?topic=161376.msg155797217#msg155797217
there ya go ... 

After going through the above post, my RAW HM1000x will shoot (18.13 JSB) 900 fps down to almost 100 bar (according to bottle) with my low powered SSG.  Now I'm not sure if the SSG would be considered to have too much hammer for your above scenario?  As you know, there's not much hammer adjustment with a SSG.

I had adjusted my set-point to 117 bar because I didn't want to deviate too much from the OEM setting of 140/150 bar.  My main pellet of choice is the 18.13 JSB, but I plan to shoot 25.39 pellets too ... so didn't want to go to low as they will need more pressure.

Unfortunately, it seems from your scenario my current 117 bar set-point is too high for the 18.13's.

Keep in mind, I have set all my QB's and BAM B50 on the knee of the curve using a RVA which was easy.

I think trying to get the best hammer/valve balance is impossible if I'm trying to shoot two very different pellets (18.13/25.39).  The knee of the curve for the 18.13 maybe 105/110 bar whereas the knee for 25.39 maybe around 125/135 bar.

Precision (ES) with one caliber (18.13) doesn't equate to even functionality in 25.39 . 
That's if you define functionality in 25.39 caliber to be between 850 and 920 fps.


 

[nervoustrigger]

For two disparate weights like the 18.1gr and 25.4gr, the knee will indeed be found at a slightly different level of hammer strike because the heavier one spends more time in the barrel and will therefore benefit from additional lift and dwell.
 
However it’s not as though the 18.1gr has an inherent knee at 105-110 bar, nor does the 25.4gr have an inherent knee at 125-135 bar.  It may indeed be that you want to run them each at different pressures to achieve a particular velocity but otherwise there is nothing that links them to a certain pressure.  Whatever the setpoint happens to be, the knee is simply where ever you find it.
 
I hope that’s not putting too fine a point on it

[Motorhead]

Abstract bit of info that has some relativity.

My personal RAW TM-1000 has been set up as a .20 cal for several years now and with just getting some NSA 10.5 grain .177's went and put the .177 barrel back onto the rifle to see if It will shoot them better than a pellet for field target use. ( lower wind drift ideally )  So here is a real mind blower ....

Set up at a >20 FPE in .20 caliber @ 13.6 weight at 800 fps ...... Set point 105 bar, Light hammer & Light spring SSG.  On a 200 cc bottle shoots near 90 shots per fill.

Set up as a >20 FPE in .177 caliber @ 10.5 weight at 920 fps ...... Set point 140 bar, Heavy hammer & Heavy spring SSG.  On the same 200cc bottle only making @ 65 shots per fill.

RADICAL differences in efficiency and required pressure and hammer strike to get equal energy performance in a differing bore diameter / area 

[rsterne]

Kirk, your statement is only partially correct.... If you are tuning for similar FPE with both weights of pellets (ie vastly different velocity), then the knee of the curve will be in almost the same place, because you won't be changing the pressure, only the pellet weight.... Getting the best tune with both should easily be possible within the adjustment range of a typical SSG.... HOWEVER, if you are trying to tune pellets that differ in mass by 40% to the same velocity, and hence the FPE is 40% different as well, you should expect about a 40% difference in the pressure required as well.... This will likely mean a big change in the hammer spring, let alone the SSG adjustment....

It's the same as retuning an unregulated gun for a 40% power increase.... not going to happen with simple adjustments, and expecting that is unreasonable, IMO....

Bob

[SpiralGroove]

Yeah Bob,
Ideally I would aim for about:
- 34 FPE with 18.13 JSB's - 920 fps
- 47 FPE with 25.39 JSB's - 920 fps
That's about 40% difference in power/pressure required for the 40% mass increase.

Originally I was hoping for 850 fps with the 25.39's ... which was closer to possible, but like many things in life ... I'm getting greedy .  Now realizing with a single tune, the #'s don't add up . 

[SpiralGroove]

So Guys,
I have understood (I think) all the ideas presented ... Thanks
 
Here's what I did :
Increased set-point to about 127/130 bar.  Now getting between 900 and 935 fps (18.13gr) with the low powered SSG and getting between 895 and 931 fps (25.39gr) with the High powered SSG.

Hitting my increased velocity goals while disregarding ES.  I will shoot a few strings and see where they stand.
I can always apply pellet sorting and other methods to improve ES as things evolve .