For HIGHER SHOT COUNT high REG pressure(115-120 bar) or low REG pressure(85-100)

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NAIRBOG

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Feb 6, 2020
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Davao del Sur, Philippines
hello! can anyone enlighten me with this? to my understanding if we adjust a pcp on a lower regulated pressure (85-100 bar) you will need "MORE" air to launch it at 900fps,,(stronger hammer strike , more dwell time on the valve).. and if we adjust it to a higher regulated pressure (115-130 bar) , even a spit of air can already propel it at higher fps (900fps) (lesser hammer strike , less dwell time on the valve..) this confusion started after i watched (

https://www.youtube.com/watch?v=nODPDEYWMrY&t=919s) roefl's

fx impact with the new power plenum set at 85 bar and shooting at 900 fps with 200 shot counts... or is it because you can now shoot your gun until 85 bar on your main reservoir?.. 

im pertaining to a .22 cal pcp with 18.13 jsb pellets with 900 fps muzzle velocity
 
This is one of those “it depends” questions but for the most part the lower regulator pressure will yield higher shot count.



So whereas high pressure & short valve dwell will indeed give higher _efficiency_, that does not necessarily translate into higher shot count because you have a shorter pressure range to work with before it drops below the regulator’s setpoint.



The working assumption here is that the hammer strike is adjusted correctly. For any given regulator setpoint and porting, there is an optimal hammer strike that will yield the best consistency, and that comes at about 95 – 97% of peak velocity. If instead you really lean on the valve to get that last 3 – 5%, efficiency will plummet and you may get poorer shot count. 



Or if you choose to operate it way below peak velocity, you can get some crazy high efficiency. For example, downtuning from 900fps to 700fps by simply backing off the hammer strike will do that. The result is super short valve dwell which means only a teeny tiny sip of high pressure air is released. However what is happening is the system is operating at partial valve lock and consistency will be negatively impacted, giving you a high extreme spread.



The reason a larger plenum improves shot count is because there is a pressure drop in the plenum during the shot cycle. Having a larger volume of air minimizes this pressure drop, holding a higher average pressure during the shot cycle. So whereas with a smaller plenum you may have needed to use a very high regulator setpoint to compensate for the pressure drop, with a larger plenum you can lower your setpoint and still maintain the same average pressure during the shot cycle, thus increasing the useable pressure range.
 
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You need some cc of air at every shot, but you need that air very fast

Assume you have 20cc of plenum and you want 900 fps, so you put your reg at 120 bar because presurized air have more cc

With 60cc of plenum you have same quantity of air at lower bars

Thats the theory, but some details makes the reallity difficult, like barrel harmonics, valve spring, hammer spring etc

If you want higher speed than the reg can give you you take from HP side air at every shot and the pellet has left the barrel and the valve is still open (waste of air)


 
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Take the answer from @nervoustrg and frame it! Can't be explained better than that.

Here is I was thinking about it:

Controlling the _efficiency_ by raising the regulator pressure and lowering the hammer spring tension so you get a tiny sip of air to propel at high fps will not give you consistency in fps as explained before, and the reason is that the system is on partial valve lock, you will find that the fps will start increasing a tiny bit the more you shoot, and when you go out of regulator pressure, the fps will increase A LOT.

If your gun is regulated at 150 bar and you can fill your gun to 250 bar you only have 100 bars of usable pressure (for consistency) so you have to tune the system to give you whatever shot count at a given fps in that 100 bar you have. On the other hand, if you can lower the regulator pressure and keep the same fps then now you can go from 80 to 250, so the usable pressure increased from 100 bars to 170 bars, almost doubling... so now you can shoot almost double or you can now tune to a higher fps but without loosing the original shot count. 

The reason the larger plenum keep the same fps at lower pressure was explained before I was just adding another way to reason about it.
 
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This is one of those “it depends” questions but for the most part the lower regulator pressure will yield higher shot count.



So whereas high pressure & short valve dwell will indeed give higher _efficiency_, that does not necessarily translate into higher shot count because you have a shorter pressure range to work with before it drops below the regulator’s setpoint.



The working assumption here is that the hammer strike is adjusted correctly. For any given regulator setpoint and porting, there is an optimal hammer strike that will yield the best consistency, and that comes at about 95 – 97% of peak velocity. If instead you really lean on the valve to get that last 3 – 5%, efficiency will plummet and you may get poorer shot count. 



Or if you choose to operate it way below peak velocity, you can get some crazy high efficiency. For example, downtuning from 900fps to 700fps by simply backing off the hammer strike will do that. The result is super short valve dwell which means only a teeny tiny sip of high pressure air is released. However what is happening is the system is operating at partial valve lock and consistency will be negatively impacted, giving you a high extreme spread.



The reason a larger plenum improves shot count is because there is a pressure drop in the plenum during the shot cycle. Having a larger volume of air minimizes this pressure drop, holding a higher average pressure during the shot cycle. So whereas with a smaller plenum you may have needed to use a very high regulator setpoint to compensate for the pressure drop, with a larger plenum you can lower your setpoint and still maintain the same average pressure during the shot cycle, thus increasing the useable pressure range.
Click to expand...


Excellent explanation. Thanks.
 
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whew! im really glad i posted my dilemma in here.. ive learned a lot from your answers guys... it really makes sense now....

OK,, the way to achieve more shot counts is to "EXTEND" my usable pressure.. this is attainable through reducing my regulator pressure to the lowest it can give, in addition , i could also achieve more consistency because there's less pressure inside the valve to work with (preventing partial valve lock) , in addition, it also lessens wear and tear of the internals as well..

i have a an fx impact MK2 , just bought it last december 2019, i could reach 900 fps at 100 bar with the power setting to max( already adjusted the tiny bolt) and the bumper to roughly 3.5 lines, but i adjusted it to 112 bar and reduced the power setting to 4 and the bumper to roughly 3 lines., the xtreme spread is almost the same at 8-10 fps , what i have now is a lesser hammer vibration and cocking effort with my current setting... also its more quiet than before..... what would you guys recommend then? havent counted the shot counts yet but with my new learnings, im sure it can achieve more shot counts on 100 bar reg...

only tested it so far at 50 yards furthest... havent shot it at a 100 yards...
 
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Not a big difference between 100 and 112 bars. But if Im tuning I'll go with the setting that allows less tension on the hammer spring. I don't own an Impact and I know that gun has multiple adjustments other than the HST.

But to me 112 is the best pressure but you need to test more because maybe at 120/125 you find a sweet spot for pressure/ HST and consistency
 
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whew! im really glad i posted my dilemma in here.. ive learned a lot from your answers guys... it really makes sense now....

OK,, the way to achieve more shot counts is to "EXTEND" my usable pressure.. this is attainable through reducing my regulator pressure to the lowest it can give, in addition , i could also achieve more consistency because there's less pressure inside the valve to work with (preventing partial valve lock) , in addition, it also lessens wear and tear of the internals as well..

i have a an fx impact MK2 , just bought it last december 2019, i could reach 900 fps at 100 bar with the power setting to max( already adjusted the tiny bolt) and the bumper to roughly 3.5 lines, but i adjusted it to 112 bar and reduced the power setting to 4 and the bumper to roughly 3 lines., the xtreme spread is almost the same at 8-10 fps , what i have now is a lesser hammer vibration and cocking effort with my current setting... also its more quiet than before..... what would you guys recommend then? havent counted the shot counts yet but with my new learnings, im sure it can achieve more shot counts on 100 bar reg...

only tested it so far at 50 yards furthest... havent shot it at a 100 yards...
Click to expand...

The lower sound is a dead giveaway that your 2nd tune is more efficient. With the higher regulator setting it places more pressure behind the valve. Then lowering the hammer spring tension you've shorten the dwell tim on the valve. I surprised where your valve adjuster knob set differences are at 110 and 112 bar. IMHO, you may have adjusted the VA to much to fast. Ive found a 1/2 turn is a lot. Each line of index on the VA is about .005 of lift adjustment (FYI on the older stopper style va not the PPMKII style). So if your turning 1/2 turn your probably adjusting .020-.025 thousands which is a lot of adjustment. You might try turning your Va back in 1/2 turn. Then adjusting back out slowly 1/8 of a turn while shooting 5-10 shoots over the cronie.at each adjustment point. Watching you FPS spread. Your very close to have a outstanding tune. I think your on the verge of a 2-3 FPS extreme spread tune.
 
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I'm currently working on a high FPE PCP, and getting a decent shot count will be important. Bottom line for shot count at a certain FPE level is to maximize the total energy available before it falls off the regulator. To get that, you would want to set the reg pressure to be 50% of the fill pressure.

That assumes that pressure is sufficient to reach your target FPE for the airgun in question.

I'm working on a gun that will have a 4500psi fill pressure. A reg setting of 2250psi would be optimal for shot count. However, I might want to run at a higher pressure in order to maximize FPE.
 
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Sometimes the gun can be more accurate with "high" reg pressure. But I would try with low first. One example is my FX crown. I first planned to shoot at the 880fps range with a .177 barrel. When I tuned the reg for the gun to shoot with a max speed of 900-910 fps, the gun ended up being very accurate at 840fps . Lower than I was initialy planning for, and a velocity difference from max at around 60-70 fps. If I increase velocity from there with same regpressure, the groups on target opens up. If I want to shoot faster, I probably has to increase reg some and try again. That gun probably likes a higher max speed on reg, compared to the "common" 20-30fps.

What I like to do is to increase hammer until I find the max speed (and I then know the max tuning speed will be 20fps less), and start lower than the speed I was planning for. Maybe as much as 80-90 fps lower, and then increase step by step until I find where it is the most accurate. 
 
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