GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: rsterne on September 14, 2014, 04:56:27 PM
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There have been a lot of shooters who are disappointed in the initial results when first fitting a regulator to their PCP.... There are two primary reasons for this, one is that often there is not a large enough plenum (chamber) between the regulator and the valve, and the pressure at the valve seat drops during the shot to a much greater extent than in the unregulated version at the same pressure, leading to lower velocity than expected.... Assuming that is not the case, then the most common thing the shooter notices is that the shot count is much lower than he expected.... This almost always happens if the hammer strike is not reduced when the regulator is installed, and is a result of the gun having been previously tuned to peak at, say, 2200-2400 psi and now it is running on a much lower pressure, making it an air hog....
Fortunately, the solution is relatively simple, and in most cases all you need to do is reduce the preload on the hammer spring to retune the gun to the now lower pressure.... If you measure and plot the velocity while you back off the preload, and assuming the gun was previously tuned to peak at a higher pressure than what your setpoint is now, you will get a graph that looks something like this....
(http://i378.photobucket.com/albums/oo221/rsterne/QB%20on%20HPA/QB79NinjaDelrin1200_zps999456be.jpg) (http://s378.photobucket.com/user/rsterne/media/QB%20on%20HPA/QB79NinjaDelrin1200_zps999456be.jpg.html)
You will notice that as the hammer spring preload is reduced, at first there is virtually no change in the velocity (the plateau), but the efficiency increases.... Between 4-5 turns out on the adjuster (in this case) the velocity starts to drop (the knee), and then past 5 turns out it declines nearly linearly with further decreases in hammer strike (the downslope).... What you are doing, of course, is you are changing what would be the peak of the bell-curve if the gun was still unregulated.... This second graph of what the velocity does in those three regions may help you understand what is happening.... Note this second graph is using a 1500 psi setpoint and does not correlate to the graph above, other than in concept....
(http://i378.photobucket.com/albums/oo221/rsterne/Important/RegulatedvsHammerStrike_zpsc71d1304.jpg) (http://s378.photobucket.com/user/rsterne/media/Important/RegulatedvsHammerStrike_zpsc71d1304.jpg.html)
First of all you will notice that when the gun is tuned on the "plateau", which it likely would be with the original, unregulated, setup, there is a slight slope to the velocity as the tank pressure drops due to the output pressure of the regulator creeping.... This is common in most regulators, more severe in some designs than others, but is usually present, and the output may be 4-8% higher when the tank is full than when it is at the setpoint pressure.... Since the gun was tuned to peak at 2200-2400 psi, it is well down on the downslope of it's unregulated bell-curve, so small drops in pressure will (usually) cause the velocity to drop slightly.... Then when the tank pressure reaches the setpoint (in this case 1500 psi) the velocity starts to drop rapidly with decreasing tank pressure.... Remember, that since the efficiency is also low when the regulated gun is working up on the plateau, the shot count will suffer.... If the hammer strike is very high for the pressure, the chance of air-wasting hammer bounce is increased, and the gun becomes a real air-hog....
If the hammer strike is reduced to retune the gun to the "knee", what you have done is effectively tuned the gun as if it was unregulated with the peak of the velocity curve at, or very near to, the setpoint.... This means that from a full tank to about 100 psi below the setpoint, the gun is operating right in the "sweet spot", and the chance of hammer bounce is much reduced.... and the velocity variation is virtually nil (in fact usually due only to pellet variations).... You have given up only a few fps and may have doubled your shot count.... This is the way I tune ALL my regulated guns....
If you further reduce the hammer strike, you are now operating on the "downslope" (eg. at 6 turns out on the previous graph).... The velocity is significantly lower, and as the tank pressure drops, the velocity usually shows a slight rise until you hit the setpoint (due to regulator creep), at which point it then increases significantly before dropping off.... The peak of that bump in the velocity is where you have now tuned the gun to if it were unregulated, in this case 1200-1300 psi.... While the gun is shooting above the setpoint pressure, it will be VERY efficient, with virtually no chance of hammer bounce occurring, and this is a good tune for target shooting, or something like FT, with one exception.... that jump in velocity below the setpoint.... If you are competing in a class where the FPE is limited and have the gun tuned for, say, 19 FPE when it is above the setpoint and they check your velocity at the end of the course and the pressure is below the setpoint you could be over the allowable FPE level.... It could also cause you to start missing targets due the increase in velocity you weren't expecting....
I personally ALWAYS tune my regulated PCPs to the knee of the curve, ie I back off the hammer spring preload until the velocity just starts to drop (3-5% below the plateau is about right).... Generally that extends my shot string 100-200 psi below the setpoint, giving me additional shots on top of the already efficient setup.... If the gun is shooting harder than I want, then I reduce the regulator setpoint a bit, reduce the hammer preload to get back to the (now lower) knee of the curve.... and end up with even more shots.... Yes, I could just back off the preload, but then I have to worry about that bump in the velocity curve below the setpoint, so instead I drop the regulator setpoint and retune to the new knee....
Bob
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Very cool. I always turn the hammer spring tension down until I find the "knee" you are talking about on the chrono and that is where that particular rifle is happy. Now I know the theory behind it. I always figured if I can get same velocity with less air usage that was a good thing. Usually the noise level goes down a bit too - but that depends a lot on hammer weight and preload.
Thanks Bob !
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Great info Bob. I think A lot of people will find it helpful.
I just went through something similar with my AA MPR the only problem is that this gun does not have a preload adjuster but you can adjust the valve spring tension. This is a bit harder because you have to degas to adjust. I went through a lot of air to get it right.
for got to mention:
I just built a regulated disco were the reg is set to 1600psi. I'm getting 1.54 efficiency. I was surprise because all the specs are the name as on mine but mine gets 1.0.
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While I'm a long way from putting in a regulator, this fits in with your other writings like a puzzle piece. I'm thinking that it would be very good to see a collection of your technical posts in print.
Thanks.
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While I'm a long way from putting in a regulator, this fits in with your other writings like a puzzle piece. I'm thinking that it would be very good to see a collection of your technical posts in print.
Thanks.
The other day someone else on another forum of wondered why the GTA didn't have a best rsterne gate
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Thanks for another cookie, Professor ;)
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Great info. It took a lot of trial and error to get my HW100 where I wanted it. Now that I read this post, what I did makes things a lot clearer.
Tom
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I'd say sticky this, it will save people a lot of time when they try to tune their regulated guns (been there, done that, got the same results).
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thank you for the write up. tagging this for after I have had my hot tea and brain cells start working.
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I'm wondering why he doesn't write a book! These days you can self publish on Amazon without spending anything but time, if you can self edit. You set the pricing once the cost to produce is discovered. You buy your own book at cost and resale if you want or it is print on demand. Print on demand leaves you no out of pocket expenditure and Amazon sends you a check or deposits into an account. I'm currently writing one now on topics unrelated to airguns. Finding time to write and note editing as i write, is the hard part for me. editing while writing causes departure from train of thought and ends up wasting time.
everyone say it with me!!! ;D
Bob
Write a book!
Write a book!
;D ;D
It would be nice for someone to publish a consolidated source of information. I'd be willing to bet a good part of the engineers that work for the manufacturers don't know their product as well as Bob. Thanks a Million Bob for all that you do.
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NO TIME !!!
Bob
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There have been a lot of shooters who are disappointed in the initial results when first fitting a regulator to their PCP.... There are two primary reasons for this, one is that often there is not a large enough plenum (chamber) between the regulator and the valve, and the pressure at the valve seat drops during the shot to a much greater extent than in the unregulated version at the same pressure, leading to lower velocity than expected.... Assuming that is not the case, then the most common thing the shooter notices is that the shot count is much lower than he expected.... This almost always happens if the hammer strike is not reduced when the regulator is installed, and is a result of the gun having been previously tuned to peak at, say, 2200-2400 psi and now it is running on a much lower pressure, making it an air hog....
Fortunately, the solution is relatively simple, and in most cases all you need to do is reduce the preload on the hammer spring to retune the gun to the now lower pressure.... If you measure and plot the velocity while you back off the preload, and assuming the gun was previously tuned to peak at a higher pressure than what your setpoint is now, you will get a graph that looks something like this....
(http://i378.photobucket.com/albums/oo221/rsterne/QB%20on%20HPA/QB79NinjaDelrin1200_zps999456be.jpg) (http://s378.photobucket.com/user/rsterne/media/QB%20on%20HPA/QB79NinjaDelrin1200_zps999456be.jpg.html)
You will notice that as the hammer spring preload is reduced, at first there is virtually no change in the velocity (the plateau), but the efficiency increases.... Between 4-5 turns out on the adjuster (in this case) the velocity starts to drop (the knee), and then past 5 turns out it declines nearly linearly with further decreases in hammer strike (the downslope).... What you are doing, of course, is you are changing what would be the peak of the bell-curve if the gun was still unregulated.... This second graph of what the velocity does in those three regions may help you understand what is happening.... Note this second graph is using a 1500 psi setpoint and does not correlate to the graph above, other than in concept....
(http://i378.photobucket.com/albums/oo221/rsterne/Important/RegulatedvsHammerStrike_zpsc71d1304.jpg) (http://s378.photobucket.com/user/rsterne/media/Important/RegulatedvsHammerStrike_zpsc71d1304.jpg.html)
First of all you will notice that when the gun is tuned on the "plateau", which it likely would be with the original, unregulated, setup, there is a slight slope to the velocity as the tank pressure drops due to the output pressure of the regulator creeping.... This is common in most regulators, more severe in some designs than others, but is usually present, and the output may be 4-8% higher when the tank is full than when it is at the setpoint pressure.... Since the gun was tuned to peak at 2200-2400 psi, it is well down on the downslope of it's unregulated bell-curve, so small drops in pressure will (usually) cause the velocity to drop slightly.... Then when the tank pressure reaches the setpoint (in this case 1500 psi) the velocity starts to drop rapidly with decreasing tank pressure.... Remember, that since the efficiency is also low when the regulated gun is working up on the plateau, the shot count will suffer.... If the hammer strike is very high for the pressure, the chance of air-wasting hammer bounce is increased, and the gun becomes a real air-hog....
If the hammer strike is reduced to retune the gun to the "knee", what you have done is effectively tuned the gun as if it was unregulated with the peak of the velocity curve at, or very near to, the setpoint.... This means that from a full tank to about 100 psi below the setpoint, the gun is operating right in the "sweet spot", and the chance of hammer bounce is much reduced.... and the velocity variation is virtually nil (in fact usually due only to pellet variations).... You have given up only a few fps and may have doubled your shot count.... This is the way I tune ALL my regulated guns....
If you further reduce the hammer strike, you are now operating on the "downslope" (eg. at 6 turns out on the previous graph).... The velocity is significantly lower, and as the tank pressure drops, the velocity usually shows a slight rise until you hit the setpoint (due to regulator creep), at which point it then increases significantly before dropping off.... The peak of that bump in the velocity is where you have now tuned the gun to if it were unregulated, in this case 1200-1300 psi.... While the gun is shooting above the setpoint pressure, it will be VERY efficient, with virtually no chance of hammer bounce occurring, and this is a good tune for target shooting, or something like FT, with one exception.... that jump in velocity below the setpoint.... If you are competing in a class where the FPE is limited and have the gun tuned for, say, 19 FPE when it is above the setpoint and they check your velocity at the end of the course and the pressure is below the setpoint you could be over the allowable FPE level.... It could also cause you to start missing targets due the increase in velocity you weren't expecting....
I personally ALWAYS tune my regulated PCPs to the knee of the curve, ie I back off the hammer spring preload until the velocity just starts to drop.... Generally that extends my shot string 100-200 psi below the setpoint, giving me additional shots on top of the already efficient setup.... If the gun is shooting harder than I want, then I reduce the regulator setpoint a bit, reduce the hammer preload to get back to the (now lower) knee of the curve.... and end up with even more shots.... Yes, I could just back off the preload, but then I have to worry about that bump in the velocity curve below the setpoint, so instead I drop the regulator setpoint and retune to the new knee....
Bob
bob , i learned a lot with tuning a regulated rifle from you...at the second graph i see that the knee you dropped the mv at 3% 910-880, and the downslope at 12% 910-800,.. can a tuner use this percentages as a guideline before doing a complete string? and do you have more data on that at different reg outputs?
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Great inffo as usual brother! I am in the process of regulating my condor and this info will help for sure.
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plinker.... The second graph was not taken from actual data, I drew it to show the trends ONLY.... However, the first graph, on the QB, was from data, and I ended up running that gun at about 4.5 turns out, at about 845 fps.... so only down about 15 fps from the plateau, ie about 2%.... Other guns will be a bit lower to find an efficient point on the knee, it all becomes a matter of balancing shot count vs. velocity.... Here is a similar graph for my 2560....
(http://i378.photobucket.com/albums/oo221/rsterne/22%20PCP/2560HPAVelocity1800.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20PCP/2560HPAVelocity1800.jpg.html)
I tuned that gun for 950 fps, achieving this shot string at 1.01 FPE/CI.... about 4% below the plateau velocity....
(http://i378.photobucket.com/albums/oo221/rsterne/22%20PCP/2560ShotString1800.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20PCP/2560ShotString1800.jpg.html)
That represents an approximate range below the plateau for the knee.... 3% might be an average drop, certainly well worth it from a shot count and efficiency point of view.... With really powerful guns (which tend to use a lot of air) you may have to drop 5% below the plateau to get the shot count you want.... and the plenum size relative to the FPE may have to do with how far you have to drop as well.... Some guns won't provide a perfectly flat plateau, it will still have a slight slope to it, and some actually lose a bit of velocity with big increases in hammer spring preload, but finding the point where the plateau and the downslope transition, ie the knee, is the important part anyway..... Your ideal tune will be somewhere on that curved portion, exactly where is a matter of personal choice, balancing power vs. shot count....
Bob
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Then it gets more complicated. Bob has the 2D version out with only preload as a variable...add hammer mass, and spring constant and it should be possible to get to a maximum efficiency for a given velocity. Speed up a lighter hammer and the valve opens faster, closes faster, and preload can be just a bit on the negative side of zero.
cheers,
Douglas
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Here is some actual data from a .177 cal Int'l FT rifle of 12 FPE that I built a couple of years ago, showing the velocity rise below the 1500 psi setpoint....
(http://i378.photobucket.com/albums/oo221/rsterne/177%20PCP%20HFT/IntlFTPCP001.jpg) (http://s378.photobucket.com/user/rsterne/media/177%20PCP%20HFT/IntlFTPCP001.jpg.html)
The velocity crept up from 800 fps at 3000 psi to 820 fps at 1500, at which point the air usage increased slightly, the velocity increased to peak at 843 fps at 1200 psi, and then dropped, getting back down to the 800 fps where it started at only 800 psi.... This rifle is a classic example of tuning a regulated PCP on the downslope....
Yes, the gun really did get 250 shots from 3000 psi down to 800 on a 13CI tank.... Each data point on the above graph is the average of 10 shots.... I ended up reducing the setpoint pressure and hammer spring preload to flatten the curve....
Bob
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Here is some more data which you may find useful.... It shows what happens when you change pellet weight in a regulated PCP....
(http://i378.photobucket.com/albums/oo221/rsterne/22%20PCP/2260PCP12Final.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20PCP/2260PCP12Final.jpg.html)
As you can see, the position of the knee shifts to more preload as you increase pellet weight.... With 12 gr. Hobbies, it is at about 4 turns out, with 18 gr. Heavies it is at about 2 turns out, and with EunJins the knee cannot be reached even with the hammer spring at coil bind.... Doing testing such as this and graphing the results gives you a complete picture of exactly what is happening inside your regulated PCP.... It is worth doing just for the learning experience alone, at least once....
Bob
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bob thanks for the inputs , i did some of the graphs already as with hammer preload vs mv , got it from the qb79 hpa conversion@1200psi output the one you made.. i think i had the same experience with the down slope, knee, and max settings was kinda vague at that time... now i see some light hehehe thanks again
mel
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Rsterne, you are kicking out almost as much power with your 2560 as I am my 22 cal condor is at 2300-2650 psi and same weight pellets. But you are getting more shots. How big is your tank and how long is the barrel? That's very interesting.
With my condor build I was shooting for the same power, around 55 fpe with 25.4 gr monsters and would like to get the same shot count as you, mid 30's is good. My biggest concern is accuracy. Keeping velocity constant helps maintain accuracy which is why I'm really researching a regulator setup.
With the info posted here is seems is should be possible with a lower pressure and get a higher shot count.
This is very interesting and making me itch even more to really dig into this project and move past all the research to my favorite part of every project! BUYING PARTS!
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My 2560 has a 17 CI tank (279 cc) and a 13.8" LW barrel.... but don't forget it's .25 cal.... Same weight pellets in a smaller caliber requires more pressure....
Bob
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There is still a basic lack of understanding about tuning regulated PCPs, so I thought I would bump this thread....
Bob
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Awesome thread Bob!
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thank you for the information. I may try the regulator I have for my disco again just to be 120% certain my disco shoots a better ES without the reg than with it.
tagging for later
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Thanks for this information. I will be needing it in the near term.
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Great post Bob :D
So, I've eventually gotten around to cutting the Mrod .25 tube and installing the JDS adapter...
The Mrod is so far out of balance its crazy.
To get it to balance right at 2000psi, I'm going to have to change a few of things.
The valve spring is violent, so it uses a sledge hammer... and so the hammer spring is way more
than it needs to be... and so we go.... I need a lighter hammer, I've already reduced the valve
spring strength and ported it and backed the stock hammer spring off as far as it'll go, I need more.... or in this case, less
;) The velocity is pretty low, only 835fps with JSB Kings @ 25.4gr and the shot count is bad, only giving
30+ full power shots off 22ci tank.
The 850's gives over 850fps and over 50 shots with the same setup.
Still, it has improved. It started out at 815fps for 28 full power shots. I think I'm almost there. It does
have a shorter barrel than the 850, so that would at least account for some of the the lower velocity.
I just need the get the valve to shut faster.
Reducing the hammer weight will help bring it to it's knee ;) and hopefully quit being such an air hog.
I'm happy with the velocity, it's right where it was at unregulated at 2000psi with the ports opened up
so I'm not expecting much more out of it at this setpoint.... just a lot more shots...
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The first thing I do now when I assemble a regulated PCP is graph out the velocity vs. preload curve, for two reasons....
1. It tell me what the absolute maximum velocity is with that combination of setpoint pressure, barrel length, porting and pellet for that gun....
2. It tells me where the knee of the curve is, which allows me to decide if I need to change the setpoint pressure to meet my goals....
Bob
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This is frustrating, we've had rolling power outages due to all this rain and flooding.
It's making it hard to get any work done at all.
I agree with you Bob. I'll reduce the hammer weight a bit at a time and let you know
what happens. The thing is so heavy it's resulting in too much dwell... it takes too long to
turn all that energy around and come back, leaving the valve open too long.
The super heavy valve spring they used was just a brute force way to "overcome" the problem... and
it's still too slow.
I'll fix it ;)
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The nice thing about plotting out the knee is that you only need 2-3 shots at each preload setting, not a whole string.... you can likely do the whole curve on one fill.... All you are interested in is getting the curve.... Once you have that, if you find you can't get down to the knee because of too much hammer strike, then I would look at reducing hammer weight.... I don't like shortening the stroke.... that just means a stronger spring and harder to cock....
Bob
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I regulated my Disco Double and followed Bob's notes from other writings he did on regulating. I wanted Higher power at around 30 FPE and about 920 FPS, so I tested my unregulated (3000 PSI) Disco first and found that if I set my Regulator at 1800 PSI I was just below the top of my bell curve
knee! I do believe I can get around 30 to 35 good shots were as before regulating I got around 40 or so shots. But the very level FPS sure makes up for the difference. I did not measure my Plenum so I don't know really how much I have, I do believe I have just a little too much or it's right on the money, the reason I say this is that if I adjust my hammer tension I do not see the velocity change or stop increasing as I screw my power adjuster all the way up, I think I just got lucky and hit it right on the money at full tension. If I turn it down 1 turn the velocity drops a little. I did adjust it to full tension then backed it off about a half turn or so and locked it down.
Anyway, my Disco Double is modified to accept a 3000 PSI fill and shoots JSB's 15.9s at 920 fps into dime size groups all day at 40 yards! Well on good days I should say lol
Anyway below is some Pics of what I did following Bob's technical data he wrote up. The Plenum OD is the same as the ID of the air tube and not very thick at all (about .030").
The second Pic is one I photoshopped to show someone how it all sets inside the air tube of a single tube or Double tube Disco.
Thanks Bob for all the great info, it really paid off for me.
William
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You plenum looks about right for 30 FPE.... If you can't get to the plateau on the curve, then you are just a bit shy on hammer strike, but since you need to back down from the plateau onto the knee to get the efficiency up it doesn't matter.... If I misunderstood and you are up on the plateau, then backing the preload down a bit will give you more shots, but with a slight loss in velocity of course.... Being happy with your tune is all that really matters....
Bob
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I have asked Bob in a pm for help tuning my S10 and he gave me the info I needed to head in the right direction. I didnt get a negative message back saying hey dummy search this and it will tell you. Instead he politely gave me the same info he has probably typed out thousands of times as if he has never had to repeat himself so many thanks to you Bob for spending so much effort and handing out all the info and research you have for the forum and having the patience to revisit the info time and time again to clear things up!!
Now I still have a quick question and I am sry if it is already answered somewhere. My S10 doesnt have a preload adjustment you have to use shims so its more of a pain and takes a little longer. I finally sourced some .034 shims so I could get a solid efficient tune. The question is if you want to tune on the knee how far down the knee do you normally want to settle at? I hope that makes sense.
Here is my data from my tuning.
Shim thickness Velocity
.085 790
.052 790
.034 790
.000 (no shim) 782
So its obvious 790 is the plateau with the current reg setting and it appears that using no shim and hitting 782 I just started into the knee. In your opinion is that far enough to gain very many shots or would dropping it a little more be better? I dont mind dropping down to 745 fps with this setup. If you think it would be better to be a little farther down the knee I could do two things. First I could cut the spring to lighten it and second I could slightly raise my reg setting. My goal is 10 - 11 fpe with as many shots as possible. I had way to much pre tension and my shot count went down badly. I should be around 200 shots and the excess pre load dropped it to 50 - 60 shots >:( I was currently using the .054 shim and thats way more than needed based on the real data I finally recorded. Thanks for any help.
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Every reduction in shim while on the plateau will save air, so just running no shim, and dropping off the plateau onto the knee, will have saved a ton of air compared with 0.085".... If you are happy with the number of shots at zero preload, I'd leave it alone.... If you want more shots, and can accept a lower velocity, then you need to cut the spring a bit to drop down lower on the knee of the curve, and then you may need to shim it slightly if you go too far....
Increasing the pressure will move you down further onto the new, higher knee, but that will increase your velocity from where you are now.... My guess is that with the combination of more velocity and a higher setpoint (less headroom) you will lose a few shots instead of gaining.... Since you are already seeing the top of the knee, and can stand lowering the velocity slightly and still have the power you want, I would leave the pressure alone and clip the spring slightly....
Bob
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Thank you very much Bob. That makes sense but this is my first regulated rifle and its not really a do it yourself type either and you have helped a ton!
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You plenum looks about right for 30 FPE.... If you can't get to the plateau on the curve, then you are just a bit shy on hammer strike, but since you need to back down from the plateau onto the knee to get the efficiency up it doesn't matter.... If I misunderstood and you are up on the plateau, then backing the preload down a bit will give you more shots, but with a slight loss in velocity of course.... Being happy with your tune is all that really matters....
Bob
I think I am not wording it correctly! I set it at 1800 PSI and that is a little lower than my Highest FPS. I guess the Pic of the shot string below will explain better what I mean!
William
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That shot string appears to be unregulated... There is no "knee" in an unregulated string, it is a bell-curve.... The knee I am referring to is explained in the first post of this thread.... You can only find it at a constant pressure (ie regulated or tethered)....
Bob
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That shot string appears to be unregulated... There is no "knee" in an unregulated string, it is a bell-curve.... The knee I am referring to is explained in the first post of this thread.... You can only find it at a constant pressure (ie regulated or tethered)....
Bob
You are correct, I did not understand or explain very well what I was saying. The unregulated shot string is what I used in reference to getting a set point of 1800 PSI just below the top of the bell curve.
William
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I agree that based on that unregulated shot string, 1800 psi was a good choice.... The fact that you got close to the same velocity means you have enough plenum volume....
Bob
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Is there a relationship between regulator setpoint and hammer weight?
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Sort of.... There is a relationship between regulator setpoint and the optimum hammer strike.... Hammer strike is a combination of hammer weight, travel, and average spring force.... Hammer travel and spring force affect both hammer energy (lift) and momentum (dwell).... Hammer weight only affects the momentum (dwell).... Generally, if you are regulating a PCP that originally operated at, say, 3000 psi.... and using a setpoint of, say 1500 psi.... you have to drastically reduce the total hammer strike or you will be wasting air.... That is the primary message of this thread.... You can reduce hammer strike by reducing any or all of hammer travel, weight, and spring force.... Motorhead has found that for many PCPs, when you fit a regulator, they work much better with a lighter hammer.... The downside is that if you make the hammer too light, you will have to then increase the travel, or spring force, to compensate.... This can become an issue in high-powered PCPs, as if may make the gun difficult to cock....
Bob
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Thanks.
Thought I had seen a hammer weight chart on GTA but I couldn't find it. Robert Lane supplied a nice chart though:
https://drive.google.com/file/d/0Bwq6Dt-mzmR9NDY5b0psaHlCeWZJSHFsUEU3bVEwWlZRQ3FN/view?usp=sharing
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NO TIME !!!
Bob
;D
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so if you have your hammer preload set as low as possible and still cant reduce velocity that means you still have not reached the knee? and what would be the solution?
I'm guessing either a lightened hammer or a weaker spring? or should I increase the set point?
nevermind, I should have read a few more posts and my question would have been answered
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Yes, if you are stuck on the plateau and can't get down to the knee, you have two choices....
1. If you want more power, increase the setpoint....
2. If you have the power you want, and wish to increase your shot count.... reduce the hammer strike by lightening the hammer, shortening the throw, or installing a weaker or shorter spring....
or, of course you can just leave it, and enjoy what you have....
Bob
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I like the way you have laid this out so people can understand the dynamics of the importance of Matching striker momentum to the pressure and output so it is in sinc.
I have tuned the Regged guns similarly lately & with the addition of the transfer port restrictor to the set-up you outlined, you can see a noticeable shot count improvement and also have the benefit of keeping the velocity from increasing as it comes off the reg.
We can change hammer weight and spring tension as well as port flow. That control is important and is why an external hammer with a threaded boss for adding weight is a key tuning feature!.
TimmyMac1
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Thanks, Tim.... high praise indeed....
Bob
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This thread should be sticky...
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I second the sticky request. it is great reference material. as is most of bob's stuff
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so a simple test to see if you are on the downslope or the plateau, would be to shoot over the crony until well below the set point. and if you are on the downslope you would see a jump in velocity as you fall off the reg. and if on the plateau would see a sharp decreace in velocity when you fall off the reg. and if on the knee it would be a smooth transition with a smooth fall as you come off the reg.
does this sound right or am I misunderstanding something?
also are there any concerns I should have with milling or simply cross drilling the hammer in my at44, other than needing to add weight back for some reason?
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sometimesyou would notice the down slope even before you reach the set point
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Jeff76; I'm not conversant with the AT44, but if the hammer is case hardened then you probably won't be able to drill or mill it as it will break tools. Grinding works.
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jeff76.... Good analysis.... as you approach and fall through the setpoint:
On the plateau (thigh) the velocity falls quickly, possibly starting it's decline slightly above the setpoint if you have way too much hammer strike....
On the downslope (shin) the velocity rises noticeably as you pass the setpoint before falling after the pressure is some distance below the setpoint....
On the knee the velocity holds nearly constant, perhaps rising slighty, as you pass through the setpoint, before falling gently, then more rapidly....
When you are on the knee, the closer you are to the plateau the less chance of the velocity rising, and it will start to fall just below the setpoint.... If you are closer to the downslope, you will get a larger velocity rise, extending the usable shot count well below the setpoint, before the velocity drops too far to be usable.... When the rise is about 1% ES, that results in the highest shot usable shot count for that setpoint for most conditions....
Bob
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I like the way you have laid this out so people can understand the dynamics of the importance of Matching striker momentum to the pressure and output so it is in sinc.
I have tuned the Regged guns similarly lately & with the addition of the transfer port restrictor to the set-up you outlined, you can see a noticeable shot count improvement and also have the benefit of keeping the velocity from increasing as it comes off the reg.
We can change hammer weight and spring tension as well as port flow. That control is important and is why an external hammer with a threaded boss for adding weight is a key tuning feature!.
TimmyMac1
I understand how the hammers energy relates to setting up the reg and getting the correct energy balanced with the reg output to be on the knee, plateau or the downslope depending on how you want to have it tuned. What I dont know is how the transfer port relates to the setup and how to utilize it to increase the efficiency. I have an S510 that I just put a Huma in. I got it installed and started to shoot with everything stock and the transfer port fully open. I quickly found out the stock S510 has way to much hammer energy for the Huma set point of 135 bar. I got 13 shots with an average of 875 fps with 18 gr. JSB. So I trimmed the hammer down to lighten it to 36 grams from the original weight of 49.5 grams. I shot a few over the chrony and it was still at 875 fps so i trimmed the hammer spring one coil. That gave me 836 fps and 27 shots with the transfer port fully open. So I trimmed another half coil and it dropped to 795 fps average for well over 40 shots with the transfer port fully open but that put me on the downslope instead of the knee and I got a sharp rise that made the ES to large over the shot string. The velocity climbed to 825 fps after dropping off the reg then stabilized for a few shots and then started dropping back to 795. So I shimmed it back to 835 fps and retained the 27 shots with an acceptable ES but I think I can shrink it some with a little tweaking.
So here is my question: My thought is if I could get my velocity to be 815 fps avg on the reg I should get a very small increase when it falls off the reg that would climb to the 825 fps and start back down to 815 fps. Is this correct? The other question is what will closing the transfer port do for my efficiency? If I start closing up the transfer port to decrease my velocity instead of reducing the shim will it give better efficiency? or will it increase shot count?
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My thought is if I could get my velocity to be 815 fps avg on the reg I should get a very small increase when it falls off the reg that would climb to the 825 fps and start back down to 815 fps. Is this correct?
Close.... Since you will need more preload to get 815 fps instead of 795 fps, when it comes off the reg. it will climb to more than 825 fps.... You will probably have to tune it to about 820-825 fps to limit the rise to 1%, but I'm just guessing without seeing the shot strings.... Your 836 setting is probably really close, I mean after all, you already doubled the shot count compared to what you had at 875 fps, with only a 4% loss in velocity.... If you leave that hammer setting, or just a whisker less, and then choke up the transfer port to get the velocity you want you should have pretty good efficiency.... The alternative is to leave the transfer port wide open, reduce the setpoint pressure to drop the velocity, and then reduce the preload slightly to get back to the new, lower knee....
Bob
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thats kinda what I was thinking Bob. The S510 is kinda a pain to change hammer settings because you have to tear it down so far to get to the spring. So if adjusting the transfer port to get that final tweaking done will work it makes it allot easier to do compared to adjusting the spring tension. I guess the one way to find out would be to choke the transfer port a little and see how it does. Thanks for the info.
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Closing up the transfer port on your 836 fps setting will reduce the velocity.... You can expect to keep the total FPE of the string at least the same as you have now.... If I understand you correctly, that is 27 shots of 28 FPE = 756 FPE total.... If you reduce the power to 25 FPE (~790 fps) you should get at least 30 shots, but maybe 31 or 32, because efficiency usually goes up a bit as the power goes down....
Bob
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i been working with breech loading rifles that are regulated..it seems that choking the port, does lower velocity..but i cant see any significant increase in shot count....but i might be wrong..i still think that output pressure, hammer strike, must be in sync.. its still better to lower output and striker wt..for lower velocities... im using the recommended..80% of the caliber as port size
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I absolutely agree that lowering the setpoint and then dropping the hammer strike is the better way to go to reduce FPE in a regulated PCP.... However, with a rifle with an adjustable port, such as the AA, it is a LOT less work to just turn it down if you are already close to what you want.... I have always found that shot count and FPE go hand in hand in PCPs, more of one is less of the other, keeping the total FPE pretty constant.... except when you push the power too high, in which case shot count decreases faster than FPE goes up.... YMMV....
Bob
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(http://i378.photobucket.com/albums/oo221/rsterne/Important/RegulatedvsHammerStrike_zpsc71d1304.jpg) (http://s378.photobucket.com/user/rsterne/media/Important/RegulatedvsHammerStrike_zpsc71d1304.jpg.html)
If you further reduce the hammer strike, you are now operating on the "downslope" (eg. at 6 turns out on the previous graph).... The velocity is significantly lower, and as the tank pressure drops, the velocity usually shows a slight rise until you hit the setpoint (due to regulator creep), at which point it then increases significantly before dropping off.... The peak of that bump in the velocity is where you have now tuned the gun to if it were unregulated, in this case 1200-1300 psi.... While the gun is shooting above the setpoint pressure, it will be VERY efficient, with virtually no chance of hammer bounce occurring, and this is a good tune for target shooting, or something like FT, with one exception.... that jump in velocity below the setpoint.... If you are competing in a class where the FPE is limited and have the gun tuned for, say, 19 FPE when it is above the setpoint and they check your velocity at the end of the course and the pressure is below the setpoint you could be over the allowable FPE level.... It could also cause you to start missing targets due the increase in velocity you weren't expecting....
Just thought I'd throw this out there for those that like to experiment. I know I won't have time to try this any time soon.
What if you were to combine the o-ring (or some other material) hammer buffer with a 'downslope' tune. Basically what the buffer can do if adjusted correctly is to chop off the top of the curve at some chosen point and significantly flatten it from that point, through the point the curve would naturally roll off anyway.
If you adjusted the buffer such that it started engaging somewhere in the region where velocity starts to rise, while still under regulation, theoretically you could flatten out the rise that occurs after it drops off of regulation and get a pretty good string, possibly all the way down to 1000 psi in the graph above.
This way you are getting the "Very efficeint" operation of downslope tuning, while preserving and perhaps even extending the number of shots available after coming off regulation.
Worth a try!
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Thats the info I was looking for. When you adjust the TP on an S510 thats unregulated to lower the fps you change the fps but it doesnt really gain shot count or efficiency at least in my experience with it. So I figured it would do the same with it regulated in that you lower the fps but basically keep the same efficiency. My fps I am getting now is fine I dont need it higher or lower but I was looking for a way to get a few more shots. If I can get 30 shots it makes it really easy to keep track of the shot count. I would also like to see my ES tighten up a little and hopefully get an ES of 10 fps instead of 15 - 17 fps. I think I neeed to polish the hammer guide and hopefully the ES will shrink. I also put a light coating of moly paste on the guide awhile back and I have read any kind of lube increases the ES on a regulated pcp. If it gets colder the lube has increased drag due to the viscosity and even in temps that dont fluctuate tuners say the lube causes a little bit of inconsistent drag shot to shot. That makes sense to me and I know on my S10 I had to remove the oil the previous owner had on the hammer to get the ES to stay consistent and under 10 fps.
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My s400 MPR ft is regulated. I balance my valve, which is a pain in the ...., to shot at 810-15 fps with jsbs 8.44. This is just over 12 fpe. Then I use the tport restrictor to bring it down to 795. I did this so I have range to fine tune. This gun is used for WFTF and I found that there is always a little fluctuation in fps depending on weather conditions. I adjust the power before a match to 795. It almost always needs ¼ to ⅛ turn one way or another. This is important to me because I click and I need my clicking to stay true.
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bstaley.... an interesting thought.... Whether O-rings are the answer, or something firmer, I don't know, but it might be worth fiddling with to find out.... The problem is, that to extend the level part of the velocity curve past the high point (ie 1300ish) you then need the buffer to get softer again.... It is typical for the plateau of the curve (above the setpoint) to increase slightly as the pressure downstream of the reg. creeps downwards a bit as the tank pressure drops, when you are using a downslope tune.... That doesn't leave much room for the velocity to increase before your ES is too great.... and of course a low ES is the reason for a regulator in the first place.... The "bump" in the velocity curve occurs when you are no longer under regulation, but below the setpoint, in a downslope tune....
Bob
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Hi Bob, and thanks for all knowledge you share.
So I fell off the fence and put a regulator in my Prod. Was set low 600fps FTTs for 30-40 shots from 2k fill down to 1k. 10lb HS, poppet cut down from 7mm to 4mm, exhaust opened .140, .140 TP. WAR NBH, TimH depinger, and 3 orings
Yesterday after installing the Milo74 regulator (I got second hand) in place of the gauge block, and putting back the original Hammer Spring no preload, took out the depinger and 3 orings, kept same hammer through(2t cw?), I filled to 1750, reg came set to 1300 the gun got 14,15 shots in the 590s before fps started falling.
Filled to 2k and set it down for a while. Pick it up later on and lost a few psi and shot 550FPS. So I filled to 3k overnight
This morning in had 2700psi and took 16, 650FPS shoots taking it down to 2475. Filled back up to 3k and see if it leaks again.
What can cause the fluctuation in velocity?
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Velocity fluctuations with a regulator are usually either a sticking hammer or a problem with the reg. itself.... It is possible for a regulator to "creep", have a slightly higher output pressure when the tank is full than near the setpoint.... That can result in either a higher or lower velocity when full, depending on the tune.... They can also "leak" slowly above the setpoint, until the pressure is high enough to seal the HP seat.... That results in a lower velocity when shooting every few seconds, and a higher velocity if you leave the gun sit for a while....
Bob
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In the case of a USED regulator and not knowing if previous owner jacked with adjustments or worse ... bottomed out adjuster screw crushing seat to seal face.
Would suspect "Set Point Creep" from a worn or damaged seat within regulator.
generally a dead give away to set point creep is that after sitting awhile ( If gauge is present ) a slightly higher pressure will read on gauge. And due to this higher pressure within plenum/valve, upon poppet being struck by hammer it become more difficult to crack the valve open and velocity of first shot will be lower.
Taking relatively quick sequential shots that shoot faster until you set gun down and wait a bit finding again the 1st shot fires slow.
Yup ... regulator seat weeping / creeping :P
** Here a copy paste made over on the Marauder forum
Re: Regulated my Prod
As asked on the GTA ... Reg set point creep may be suspect ... Or ???
Also building quite a few regulated P-rod / 1701 & 1720 regulated pistol conversions, when you take guns operating pressure within valve to @ 1300-1500# the required hammer strike really falls away !!
Factory hammers become too heavy ! and in the case of Travis's NB version, not sure where weight is relative to OEM ?
* Also if the No Bounce is setting to quickly it could be hanging valve open slightly or slowing down the closing speed screwing with valve dwell which will screw with velocity consistency.
What i would do is install OEM hammer and see if velocity instability still exists ... eliminate one part of the working system at a time until you isolate the offending part/reason.
Scott
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Cool I'll put the oem hammer back in. Should i remove some weight from the oem hammer? The NBH weights just about the same as oem. The reg came set to 1300 and wasn't messed with from what I've been told.
I shot a 3k string and got a 48 fps spread. Started at 605 648 600 last 4,5 shots fell to 578. The JB tank gauge showed it shot down to 1000psi 64 shots.
Thanks Guys
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That kind of string is what you get with an unregulated PCP, it almost looks like the regulator isn't working....
Bob
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Bob, Honestly, you do have a gift for technical writing. And all the hours and hours of designing and building and testing and analysis that you do beforehand is an incredible gift to the airgun community. Thank you, sir.
I am reviving this thread because of the guidance it is giving myself and Miguel in tuning the Marauder pistol with a Huma regulator.
http://www.gatewaytoairguns.org/GTA/index.php?topic=100748.0 (http://www.gatewaytoairguns.org/GTA/index.php?topic=100748.0)
When I first saw the Huma claim of 31 shots at 18.8fpe from a P-Rod pistol with a standard 66cc reservoir, well, I have to say I was skeptical. But with the info from Mr Andriessen from Huma, and others, and this thread, well.... I am becoming a believer. Trying to eek out every last shot from such a small reservoir, I can see where every variable must be addressed, and that for best efficiency, the gun must be tuned for one pellet weight at one velocity.
So here is the question, plenum volume? Given that the normal reservoir is only 66cc, it would be best to keep the plenum volume to a minimum (without jeopardizing fpe) so that the HP volume can be kept to the max. With the current setup, the plenum volume, including the volume inside the valve, is approximately 8 cc. Seeing that this is well below 1cc/fpe, it seems that trial and error might be the only definitive way to determine how small the plenum can be. I would assume that a higher set point would require a smallish plenum, but maybe because the practical set points will all be within a 500psi range, one plenum volume can be decided upon that will work within that range. So, to further refine the question, I guess I should first achieve my "optimum" tune, and then try whittling away at the plenum volume until the power drops, realizing that a hammer spring tweak might be needed? At some point, it will be splitting gnat's hairs, because exchanging one plenum cc for one HP cc won't yield any further improvement in shot count. Again, I can see that this is only significant in guns with tiny reservoirs.
Bob, any thoughts would be appreciated.
Thanks,
Lloyd
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Lloyd, we did a quickie analysis of this not long ago.... If you have virtually unlimited reservoir (ie a large bottle feed a plenum through a regulator), then the 1 cc per FPE that I have been recommending for a while is, IMO, still the best compromise.... Going smaller will cost you in FPE and efficiency at any given pressure, requiring you to increase the setpoint to get the FPE back.... while going larger doesn't really pay much dividends.... However, once you are using an "in-tube" regulator, and trading HP volume for plenum, things change.... It seems that around 1/2 cc per FPE is a better choice, and of course even that is flexible.... The higher the power you are trying to achieve (relative to unregulated at the same pressure), the more plenum you need.... If you are going for low power and large shot count, then you can shrink the plenum more.... Plenum volume, BTW, includes valve volume (all the air that can affect the pressure at the valve seat during the shot cycle)....
You have it exactly right, that trading HP volume for plenum will eventually find an optimum for any given FPE level.... As you increase the plenum size, you can use a lower setpoint, so even though you have less HP volume, the "overhead" (the pressure range from fill pressure to setpoint) is greater, giving you almost the same amount of air (pressure range times volume).... When you decrease the plenum size, the opposite occurs, you need to increase the setpoint, losing overhead, but gaining on HP volume.... Within small changes in plenum and setpoint, there will be several combinations that COULD produce about the same shot count at your chosen FPE.... EXCEPT....
When you tune to the correct point on the "knee" of the curve (I'm talking here about a plot of velocity vs preload).... as I started this thread with.... you end up being able to "cheat" out a few extra shots.... THAT is the combination that will prove to be the BEST for your chosen FPE level.... If your pressure is high, and you are on the downslope, your velocity below the setpoint will climb.... If your pressure is too low, and you are on the plateau, you get a sudden drop in velocity below setpoint.... However, when you find the OPTIMUM point on the knee of the curve, you get a nearly flat velocity while above setpoint, and then a VERY slight increase (a percent or so) just below setpoint, and then a gradual initial drop in velocity.... This can easily give you 10-20% more shots as the pressure drops just below the setpoint, without even noticing the ES.... IMO, that is THE best way to tune a regulated PCP.... The setpoint is JUST before where the peak of the velocity would be, unregulated....
To answer your base question, 1/2 cc per FPE is likely in the ballpark for plenum volume when using an in-tube regulator.... You will need to use a higher setpoint than what gave you your desired FPE before you put in the regulator.... For example, if you were getting 20 FPE at the bottom end of the unregulated string at 1600 psi, you will need at least 10% more pressure than that (I pulled that number out of the air).... let's say try 1800 psi for a setpoint.... Try a couple of shots at each preload setting, and plot the graph of velocity vs. preload.... DON'T get lazy, do the graph, you will learn a ton.... If you really want to understand how important the preload is to efficiency, shoot an entire string at each setting and calculate the FPE/CI.... You will find that being on the plateau is NOT where you want to be.... Pay attention to what the velocity does as you cross the setpoint, and you will find how far down the downslope you can go before the velocity rise gets too great to be usable.... Once you really UNDERSTAND what your gun is doing at 1800 psi with the size plenum you have, and what you can get for the optimum combination of FPE and shotcount at that pressure.... THEN you can decide if you need to change the setpoint or plenum size....
If after finding the optimum tune, where the velocity just seems to hang on for 200-300 psi below the setpoint, you decide you need more FPE, then you have two choices.... a higher setpoint pressure or a larger plenum.... Obviously, changing the pressure will have a much greater effect, unless your plenum is really small.... If the plenum is too small for the FPE you are trying to get, you will need to increase the setpoint more than seems reasonable.... I haven't played much with in-tube regulators, but logic tells me that if the gun is insensitive to relatively large changes in setpoint pressure, the plenum is too small (for your FPE level).... That would be because although you are changing the pressure at the BEGINNING of the shot cycle, the plenum is just too small compared to the barrel volume (and the amount of air you are using per shot) to maintain reasonable pressure throughout the shot.... Conversely, if the plenum is up around 1 cc per FPE, setpoint pressure changes will have a large effect on FPE when tuned optimally....
Bob
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Bob, Thanks for the detailed reply. It is very helpful. I have already been graphing various regulated strings with various hammer preloads, and most of them are of the shape of your downslope velocity in your first post in this thread. So it seems like i need to go back to an unregulated setup and graph the velocity vs preload at several different pressures to find the knee at the desired fpe, whatever that particular pressure turns out to be. I agree 100% that graphing the real data reveals a lot of hidden information that isn't obvious when just looking at a page of numbers. And I do understand about tuning to get those extra shots as the pressure falls off the regulator.
So here we are back at the plenum question again. I am going to go with the suggestion of about 1/2cc per desired fpe. I assume that when I am doing the initial unregulated testing to find the knee at a specific psi (vel vs hamm preload) that it would be desirable to mock up the "stingy" plenum volume within the reservoir, just as it will be when the regulator is installed. That should help to eliminate any surprises when the regulator is installed and set at the pre-determined pressure. BTW, I have a fairly accurate gage with fine enough resolution so that I can determine the actual psi used per shot during the initial unregulated testing, and thus the efficiency of each shot. The determination of an "optimum" setup can be as involved as you want it to be, I guess.
Bob, also, just as a point of reference, this is .22cal, 12" barrel, the barrel port is .125 (31% of bore area), the T-port and ex port are both .138 (39% of bore area), and the valve throat effective area is 51% of bore. I am assuming that with the short barrel, and low fpe requirement, those smallish numbers are ok.
Lloyd
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I'm not sure how you can find the "knee" in an unregulated PCP.... it requires a constant pressure to plot velocity vs. hammer preload and get a plateau, knee, and downslope.... If you are feeding the plenum in your gun from an external regulator, at constant pressure, (ie tethering the gun) then you certainly can do that.... If you have an accurate gauge, and plug the plenum to the desired volume, you should be able to determine your optimum setpoint and preload without ever installing the in-tube regulator until your testing is all done.... Adjust the setpoint, install it with the same size plenum, and you should get the same results....
I don't think you will have any problems with those port sizes.... My Grouse Gun has a 1/8" transfer port and a 14.5" barrel, and gets 20 FPE (18 gr. @ 700) unregulated from 2000 psi down to 1200....
Bob
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Bob, yes, I will be using a regulated supply to determine the the knee. That seems to be a bit easier than draining the gun and removing the reg to re-set it, then reassembling and refilling for each different pressure setting. So it does sound like doing the testing at the "final" plenum volume is essential. I will do that.
Thanks,
Lloyd
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Yes, I would definitely use the final plenum volume.... What changes is the pressure at the end of the shot, and that affects the average pressure while the valve is open, of course, and hence the velocity.... The smaller the plenum, relative to the barrel volume (well actually the volume of air used in the shot), the greater the pressure drop, and the lower the resulting velocity... It is easy to calculate, and in fact your spreadsheet can do the math quite well, just use the plenum volume for the reservoir volume.... You will quickly see what happens as you change the plenum.... and how much you need to compensate for a smaller plenum by increasing the setpoint (starting pressure).... to get back to your desired FPE....
Bob
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Here is a little bit of data related to small plenums. This is a P-rod with12" barrel, a Huma regulator, 48cc HPA, 10cc regulated plenum.
Set point was about 1740 psi, fill pressure was a bit over 3k, final pressure was abut 1600.
24 shots 18.1gn, avg vel 682fps, avg 18.7fpe, ES 10fps (1.5%), avg air efficiency approx 1.23fpe/cuin
25 shots 14.5 gn, avg vel 747fps, avg 18.0fpe, ES 10fps (1.3%), avg air efficiency approx 1.27fpe/cuin
This info is from this thread:
http://www.gatewaytoairguns.org/GTA/index.php?topic=100748.20 (http://www.gatewaytoairguns.org/GTA/index.php?topic=100748.20)
It seems like a small plenum can work in this short-barrel situation.
Llloyd
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Glad that 10 cc plenum worked out OK for you Lloyd.... what is that, about 0.55 cc per FPE (plus minus) ?.... That is the same ratio as what I have on my QB79, however when I change the tube only to a QB78 tube, with a larger plenum, I gain FPE for the same volume of air used per shot (same number of shots), so also gain efficiency.... The difference is that I don't lose HP reservoir volume when I do that because it's a bottle gun....
Bob
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This is interesting between the small plenum size and 12" barrel vs a Bottled QB with a barrel over 20".
If just calculating a 12" barrel without the extra behind it, it's just under 8cc's. A longer barrel with larger plenum would make sense for using the air more efficient to produce the same power.
Should optimized plenum size be based on desired fpe and barrel volume to be the most efficient?
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Yes, this is getting down into the splitting hairs region. It seems like it might be getting near the low limit of plenum volume for producing that power. But I think if you only wanted 12fpe from this same gun, you could probably go smaller than .5 cc/fpe.
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This is interesting between the small plenum size and 12" barrel vs a Bottled QB with a barrel over 20".
If just calculating a 12" barrel without the extra behind it, it's just under 8cc's. A longer barrel with larger plenum would make sense for using the air more efficient to produce the same power.
Should optimized plenum size be based on desired fpe and barrel volume to be the most efficient?
To produce the same power and achieve more efficiency, Probably be better suited with the longer barrel smaller plenum and higher output psi..... for the same power. The longer barrel is gonna cause the efficiency to increase by causing the velocity to increase, which is gonna require you to drop the plenum size and/or lower the psi in order to keep the fps the same. higher psi with smaller plenum seems to always increase efficiency. So in my thinking, there should be some optimal condition based on barrel volume that renders the best power to efficiency. Bob has been all over it for some time now with the 1cc/fpe and at this point I see that as law. That's not to say that it can't be done with less, but is more of a very reasonable goal when setting out to design or build a gun. Bob has also pointed out that guns that are producing higher efficiency are closing the valve around the same time that the projectile has reached ~30% of the barrel length. This would suggest that you could propel the same projectile at the same speed from a dump gun using a dump plenum of 1/3 the barrel volume at the same psi. That's not likely reality. If that were a 20", .25cal barrel, 1/3 vol would be ~7cc. The question is, can you achieve say 950fps from 7cc at 2000psi, with a 25.4gr pellet? If so, then we are flirting with reality. There are cross over characteristic between standard PCP's, regulated PCP's and Dump valve guns. I contend that when we are able to recognize and isolate the characteristics, we can then really unlock the power and efficiency of a charged gun. A regulated PCP is basically a hybrid between a pcp and a dump valve gun. Just the dump valve get refilled really quickly and that leaves us some grey area of under standing. So we are left to ponder the valve timing in a more isolated and controlled condition. I've spoken of this before and probably fail to convey or articulate the concept very well but just imagine a valve design that has a plenum that is designated with a volume, has regulated psi, and when fired, the plenum is allowed to go to zero before it is refilled. When refilled, it is refilled to a set psi, under a set volume to be cycled again. That would be as close to a square sine wave as I could imagine. The valve is open until it is empty then shuts to establish the exact same condition. Valve timing is no longer an issue and the plenum is sized according to desired performance. Tuning would be changing the regulated psi. Bigger plenums equal less efficiency but higher power potential. The question is, can we get 950fps with 7cc of air at 2000psi from a 20" barrel, shooting a 25gr pellet? If so then we can do better with a longer barrel and higher psi and a heavier slug.
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Yes, this is getting down into the splitting hairs region. It seems like it might be getting near the low limit of plenum volume for producing that power. But I think if you only wanted 12fpe from this same gun, you could probably go smaller than .5 cc/fpe.
LOL. Lloyd that might be getting cocky right there. But I do agree. In fact the power output could be decided by simply choosing a working psi (regulated) and increasing or decreasing the plenum. If you wanted a 50fpe pellet shooter, then you'd have a 7cc plenum at 2000psi and a 20" barrel. But if we wanted a slug shooter that generated 120fpe, we'd probably need something more like a 30" barrel and a 23cc plenum (which is close to 100% barrel volume). Even though, 23cc is a fairly small dose of air at 2000psi. Of course, if the psi is raised, the barrel can be shortened or the plenum made smaller. Also, if we had a slug shooter that generated 120fpe and wanted to shoot pellets, we could simply have all the features that are required to produce 120fpe. the 23cc plenum the 30" barrel but can just lower the reg psi to say 1000-1100psi and get 50fpe pellet shooter. I imagine that the efficiency would increase in comparison but would it be optimal? No not hardly.
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The question is, can we get 950fps with 7cc of air at 2000psi from a 20" barrel, shooting a 25gr pellet? If so then we can do better with a longer barrel and higher psi and a heavier slug.
Not going to happen .... 7cc's at 2000# is no longer at that pressure ever falling lower as it fills the space between valve poppet and pellet. Greater the throat area & transfer size gets, greater is the loss in pressure filling the space.
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Correct. But take all the space between the poppet and the pellet out of the equation. A chamber that is 7cc charged to 2000 psi is allowed to expand to 23cc is an exit psi of about 600ish psi. That is exerting 29lbs of force at the base of the pellet when it breaks free of the bore. The force is sufficient to attain that fps as long as the friction is 10lbs or less. I think it is for a .25 pellet.
I'm thinking outside conventional wisdom and dismissing what we are familiar with. No dead space behind the pellet and most likely an in-line flow dynamic with nozzle. Nozzle converges to .1875 only to open up to .250. No turns and throat is as close to zero length as you can get (probably need a small flat to avoid erosion or something other than Aluminum).
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The question is, can you achieve say 950fps from 7cc at 2000psi, with a 25.4gr pellet?
According to Lloyd's spreadsheet, that would require 80% efficiency (using realistic assumptions).... I've never seen that in a quarterbore.... Pressure at the muzzle of a 20" barrel would only be 607 psi maximum.... At 70% (possible), you're down to about 44 FPE.... this with a dump shot, of course.... If you eliminate all the pellet friction and transfer passage volumes, you would need 75% efficiency to get your 50 FPE.... I would say that means it's very unlikely.... Even if you could achieve instantaneous opening of the valve, the pressure pulse is far from a square wave.... After the initial pressure rise it is a steady decline as the limited reservoir volume fills the barrel....
One thing you guys may be missing.... You don't "need" a 1 cc / FPE plenum to obtain your desired FPE, you can do it with 1/2 cc / FPE, but you have to increase the setpoint pressure because the pressure drops faster during the shot.... You can likely do it with 1/4 cc / FPE as well, but be prepared to up the setpoint pressure even further.... Eventually, the plenum will be so small, you won't have a regulator (you will need full tank pressure), and you will have to keep the valve open until the pellet exits.... They call that a dump shot.... For a given starting pressure, barrel length, caliber, and volume (reservoir/valve/plenum/whatever), you will have a maximum FPE.... If you want more FPE, you can use a larger volume, to get a higher average pressure, but the efficiency will drop if you stay with that dump shot....
These are all just different versions of the same thing.... and for the most part utterly predictable using Lloyd's spreadsheet....
Bob
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Okay Gentlemen, I've been toying with my 177 Challenger FT rig. I've been shooting Hunter Class with it just under 12 FPE or 780 avg. fps with 8.44grn JSB's. Needing a flatter trajectory I've changed hammer spring, and I forget the TP size(I have several to try) At the moment I'm trying to take the velocity up in FPS until loose accuracy then back up a couple steps and use that as my starting point for a Huma regulated tune. Currently I'm at 900 avg. fps. and getting very good accuracy at 55 yards(55 is my test yardage) I'd love to get in the upper 9's with a decent shot count, or lower 9's with 10.3's. After reading this and the post about the hammer spring guide it sounds as if these two tricks are something I ought to try.
Lloyd gave me a lot to think about the plenum, is there enough area there for a plenum if the guage block were drilled out?
Would a 3k fill allow for enough shot count increase to be worth while?
Could you guys please give me some ideas you how you'd go about doing this?
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I don't know that gun but if possible Scott's LW hammer or Bob's new hammer design. Scott has made it look like voodoo with his LW hammers and it is by far the simplest solution to increasing efficiency. Probably need a combination of LW hammer and a hammer spring. I'd contact Scott (Motorhead) and discuss it with him, he is the guru on reg'ed PCP's and LW hammers and he is into the same application.
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Bob yes your right on the pressure profile, it isn't square sine at all. I could have articulated that better I suppose. The time and function (Physical movements) is pretty close. The first corner a touch rounded for opening to the certain distance. The pressure profile would look close until the certain distance was met then I think it would look more like a saw tooth..? The concept I'm toying with has as close to zero dead space as I can imagine without contouring the exit side of the nozzle to match the projectile tail profile and that isn't practical at all. The nozzle profile is 60* included on the converging side and 16* included on the diverging side, with an orifice at 3/16. That will flow an unbelievable volume of air at the pressures we are working with. I think that the peak pressure spike occurs quicker than it occurs with our typical poppet valve and with next to no dead space, acceleration is quicker. I'm using 10# of break away friction in the math. the running friction is pretty darned small and even difficult for me to measure with out building a rig to do so. Even then, I cant test or measure it anywhere close to the velocities we're moving. so it is a SWAG really, 1#.
Anyway I drug this off topic far enough. the point was that there are overlapping characteristics that can be useful if applied to the regulated PCP, that will milk the system for max efficiency.
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Any thoughts or advice to share when adding an adjustable transfer port in to the mix when dealing with a regulated PCP? I've been using a combination of hammer spring preload and choking down the transfer port in order to get a PCP down from 12fpe to about 8fpe for indoor shooting, and while I know what I did works, I am curious as to whether there was a more efficient way to do so.
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Unregulated PCPs were very often tuned for extended strings for FT work by leaning on the hammer spring and choking up the transfer port.... You can certainly reduce the power of a regulated PCP very simply by installing a smaller transfer port, and if the gun is operating efficiently before, it will generally get even higher efficiency (in FPE/CI) when the power is reduced.... and it does get quieter in proportion to the FPE reduction.... It can be done externally with a adjusting screw, if that is incorporated into the design, such as my retracting bolt that can be restricted, or the velocity screw in an MROd valve port....
You can also reduce the power, and increase the efficiency dramatically, by reducing the hammer strike (preload) to use smaller sips of air, but if you go that route, you MUST stay above the setpoint, or you will experience a drastic velocity increase once the pressure drops below the regulated output.... Look back at the first post in this thread to see what I mean.... The great thing is this is instantly adjustable and reversible without any disassembly....
The velocity can also be reduced by dropping the setpoint pressure and readjusting to the knee of the now lower curve.... This gives more shots from the greater pressure range, and increased efficiency as well, although is more complex to do, and not as easily reversible as simply dialing back the hammer preload....
Generally, the very highest efficiency is obtained by using tiny sips of high pressure.... That means the valve is closing very early, and the air is still expanding as the pellet leaves the muzzle.... The shot will be very quiet as well.... The only drawback, as I said, is the velocity increase below the setpoint.... This likely makes using reduced preload the best method to detune temporarily, just watch the pressure guage....
62hotrod, if you haven't plotted the curve of velocity vs preload for your gun, you need to do that.... If you are already near the plateau, no amount of increased hammer preload will help, and you will just use more and more air.... Without that information, I can't offer any reasonable advice.... You can obtain some plenum space by modifying or eliminating the gauge block.... I would look for about 1/2cc per FPE minimum for a gun with an in-tube regulator (about 10 cc for a 20 FPE gun).... and make sure that volume is readily accessible to (and includes) the valve....
Bob
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Bill.
What was not said 2 posts above ... is the Time/Area piece of the tuning puzzle.
It is well known as you operate at lower pressures the Area of ports must become larger than a higher pressure model operating at equal output/power.
So while I'm not stating such a small volume plenum could not be made to work in some optimized configuration,
doing so personally feel "That Tune" would be within very limited caliber & pellet weight/fit parameters.
PLEASE ... do it and share results so we can learn from it too ;D
Optimist or Pessimist ... I'm soo conflicted !!
Just do it ;D
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.............
........... The question is, can we get 950fps with 7cc of air at 2000psi from a 20" barrel, shooting a 25gr pellet? If so then we can do better with a longer barrel and higher psi and a heavier slug.
Bill G ,
I didn't actually answer your question, but I've got the vultures circling around it. Take a look at today's entry in this thread:
http://www.gatewaytoairguns.org/GTA/index.php?topic=94054.0 (http://www.gatewaytoairguns.org/GTA/index.php?topic=94054.0)
Lloyd
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.............
........... The question is, can we get 950fps with 7cc of air at 2000psi from a 20" barrel, shooting a 25gr pellet? If so then we can do better with a longer barrel and higher psi and a heavier slug.
Bill G ,
I didn't actually answer your question, but I've got the vultures circling around it. Take a look at today's entry in this thread:
http://www.gatewaytoairguns.org/GTA/index.php?topic=94054.0 (http://www.gatewaytoairguns.org/GTA/index.php?topic=94054.0)
Lloyd
Not us !! .... Lol
(https://s.yimg.com/fz/api/res/1.2/0BnM.eDbRBPQ_kTzvBCazA--/YXBwaWQ9c3JjaGRkO2g9NTEyO3E9OTU7dz05NTg-/http://healingthoughtsblog.files.wordpress.com/2013/02/vultures-circling.jpg)
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We in trouble now! :(
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another great article
must print it and labeled "the science of PCP"
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With time comes increased clarity and understanding (ie I'm always learning).... so I thought I would revisit this subject to add a chart that might help you understand what happens as you tune a regulated PCP with progressively less velocity than the plateau.... Here is an updated version of the chart in the first post of this thread....
(http://i378.photobucket.com/albums/oo221/rsterne/Important/Regulated%20Tunes%20vs%20Hammer%20Strike_zpskwsffwma.jpg) (http://s378.photobucket.com/user/rsterne/media/Important/Regulated%20Tunes%20vs%20Hammer%20Strike_zpskwsffwma.jpg.html)
The 3%, 5% and 10% below Plateau velocities are approximate only, but will give you an idea of what happens as you reduce the hammer strike, and hence the velocity, on a regulated PCP.... It will show you exactly why I like to tune 3-5% below that plateau.... because (at about 5% down) you get a few more usable shots below the setpoint before the velocity drops off.... or at the very least (at about 3% down) you save a lot of air compared to tuning up on the plateau, with very little loss of power.... The chart also shows what happens if you tune about 10% (or more) below the plateau.... Note that below the setpoint the velocity increases significantly.... and while operating in that realm gives you extremely good efficiency, for some applications (eg. Field Target, or in some countries where there is an FPE or velocity limit) that bump could put you over the limit....
Every gun is a bit different, and yours might produce a curve like the "5%" one above only 3% below the plateau, or it might be 7% below.... but to date those would be about the outside limits I have found to produce a tune that has a usable shot string (ie within a ~1% ES) extending slightly below the setpoint, which is the tune I prefer.... I hope this chart allows you to visualize what I have tried to confer in this thread....
Bob
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You have me a bit confused(easy to do).... looking at the chart, the -3% plot clearly yields the smallest ES of the four plots.Were this one of my guns, there's little doubt that would be my goal as it would offer the best opportunity for consistent accuracy. Below the chart you indicate the -10% plot is the most "efficient"; which may be the case if one only seeks maximum number of shots, but that really disregards the whole point of how much time, money and energy we put into these things just to get them to hit the target! Just sayin...
pv
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Even the best of regulated PCPs rarely achieve an ES of less than 1%, just from pellet variation.... That is the goal I set myself when tuning, as it is plenty good enough for shooting past 100 yards, and the -5% line on the chart above shows a total ES of 1%, from the start of the string to about 1200 psi, where the velocity falls through the starting point.... I am sure that you realize that no shot string is as smooth a curve as I have represented on the chart, as there is a shot-to-shot variation of several fps superimposed on the base curve....
As I have stated before, my tunes vary between 3-5% below the plateau velocity, depending on the purpose of the tune.... If I am after maximum power without wasting air, I will be closer to the -3% curve.... but if I am less concerned with power, and more concerned about efficiency and shot count I will be closer to the -5% curve.... In addition, if you want a smaller ES, and if the tune you choose has a bit too big a bump below the setpoint.... then stop shooting at the setpoint and you will get a few less shots with a tighter ES.... You will still enjoy greater efficiency with the -5% tune than with the -3% tune, possibly by as much as 25% higher FPE/CI and shot count....
The very best .22LR target ammo has an ES of about 2.5%, with most commercial ammo 4% or more.... Our PCPs are capable of about 1% ES under the best circumstances, and since a 2% ES is fine for 100 yard work (ie the vertical stringing is well within the MOA capability of the gun and shooter).... if I can get a few more shots and keep the ES in the 1-1.5% region I am more than happy.... I defy anyone to distinguish between a 1% ES and a 2% ES at any range within 100 yards....
I don't use the -10% tune, because although it is the most efficient in terms of air use, and will produce a ton of shots.... it has a large increase in velocity below the setpoint, where the gun shoots like an unregulated PCP, with a bell-curve.... Yes, you can simply stop shooting at the setpoint, and enjoy that efficiency.... but just like a unregulated PCP in the first part of the bell-curve, the shot-to-shot variation tends to be greater throughout the string.... This is because any slight variation in hammer strike, pellet weight, or pellet fit, causes a larger velocity variation when the valve is operating in "partial valve lock".... Therefore I stay away from those tunes, just as I stay away from tuning on or near the plateau because doing that wastes so much air....
Bob
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Bob and Lloyd are both a rare gift to the modern airgun world; beyond reproach. Way back in the earliest days of big bore PCP airgun development, in the 1970s and early 1980s, I became friends with a machinist living in Arizona, who, as far as I know, developed the first American big bore air rifles, most of them in .44 to .510 caliber, to take big game. We tried Various barrel lengths, Various plenum volumes, various pressures, etc. We did a considerable amount of bullet design & alloy testing for use in those air rifles. Eventually, we received velocities very similar to modern day commercial air rifles. Back in those days, we knew nothing about regulators, or about shrouds. Even today, I hate shrouds---guns should be loud. One thing, among many things, that we learned, that surprised us, was that a certain volume percentage of air, affects velocity much more than the same percentage of pressure.
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Bob
Thank you, I think I have an understanding of your above posts.
Question,
I am just setting up to shoot the SSG and learning about the turn info, for the 22 cal QB 79, (OEM stock),
will 2-5 shots per turn be enough to gather valid info, on the SSG settings, with each of the different pellet weights, I want to use?
Now, that I have the compressor/tanks etc,
would it be better to shoot from the tethered 4500 psi tank > reg set to 3000 psi set point or 13/3000 psi tanks,
on each of the different reg set points of 850, 1100 and 1250 psi, of the 3 - 13/3000 Ninja tanks.
Tia,
Don
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I shoot 2-3 shots and record the average.... or for a quick determination of where the plateau is, just 1 shot is OK, providing you graph it out to smooth the curve.... Once you decide on where the knee is for each pressure and pellet, then you may want to shoot 10 shots or so at each setting.... enough to get a decent pressure drop so you can calculate and plot the efficiency....
You can tether your 4500 psi tank, through a 3000 psi regulator, to each of your 13 CI / 3000 psi tanks, just so you don't have to fill then frequently.... but a 13 CI tank by itself will provide a bigger pressure drop over 10 (or whatever) shots to determine the efficiency....
Bob
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Thank you, Bob
I have a very accurate psi test gauge that reads to 1/4% for the full 3000 psi range, in 20 psi steps,
with Ninja Micro bore hoses/Foster QD fittings, it is set up so I can see the psi readings on every shot fired,
when the Mag V-3 chrono is attached, along with all the SD/average for the shots fired etc.
I can shut off the 4500 psi tank and shoot from the 13/3000 tanks, then refill the 3000 tank from the 4500 tank and continue on etc.
I'll post the results for every ones view, good, bad or otherwise,
as I think I am over my head with those graphing posts you show on figuring the efficiency etc . LOL
More info later.......
Tia,
Don
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Just to share another Short cut or trick we use ... here is another less done approach.
get close via hammer spring, hammer weight to @ where ya want to be .... do a pressure test by having THE PCP hooked up too an air source starting 3-500 PSI under where your regs set too.
Shoot over the chrony changing AG's tank pressure in 100# increments noting velocity.
If you note a PEAK in velocity at a pressure LESS THAN regs set point ( being higher than baseline tune ) you know that reg is set too high.
If you notice velocity keeps increasing all the way to regs set pressure you may very well be UNDER the optimum set pressure or very close to it.
* in this case, it is beneficial to up the Regs pressure far enough to see at what pressure velocity peaks & note where it starts dropping ( WITH NO CHANGES IN HAMMER SPRING SETTING or OTHER adjustments )
In doing a pressure check you get to chart what the rise or fall is in velocity under or beyond any give pressure. Then given this data you can adjust the regulator pressure just shy of the peak getting just a tad behind the bell curve.
Just another work around getting to the same place in having your PCP able to shoot at SET PRESSURE and get some more shots beyond ...
Scott
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Scott
Thank you for your info.
I am attempting to wrap my head around this info, never seen/read about this test before.
After finishing the prelim testing of the SSG and the various pellets with a 13/3000 tank,
reg set for 850 psi, logging all info etc.
Questions,
What effect does the pellet weight play in this test, or does it matter?
Note :
I have to also test the accuracy of this OEM bbl and the various pellets and hopefully the accuracy of this bbl,
will be better than the 1-1/2" groups at 25 yds, I started with, (has a new chamber/polished bore/muzzle crown).
So, I can run the psi down to below the set point of the reg, and/or fill to the required 100 psi levels to do your tests etc,
without doing a lot of extra work/wasting air etc.
Would this be an acceptable method to test with?
Suggestions/Ideas would be greatly appreciated.
Tia,
Don
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Don,
I work with regulators so much that investing in a test gauge that goes BETWEEN my fill bottle & gun. What this allows me to do is see very precisely what the guns air tank has for pressure as it is gradually filled. * Fill valves that hang open until reverse flow happens even allows seeing how much PSI per shot guns actually doing ;)
When you shoot over the chrony UNDER the set pressure ( And if under the bell curve ) note velocity shifts with every shot.
Ideally you become aware at a certain pressure within the PCP that velocity shifts over 1/2 dozen or shots does not change at all which indicates ( As hammer is currently set and pellet weight used ) is running at the apex of the natural bell curve. ** NOTE what the pressure is !!
If the regs set point during this test is still higher you will see the velocity start dropping off as you fill to higher pressure and gives you first hand info on where velocity is headed if you get any regulator creep if you reset the regulator at that pressure.
* Also using this test gauge have the ability to hook it up to my Regulator test fixture and see a particular regulators Creep tendency.
Armed with knowing what the Creep / Pressure drift is on a specific regulator along with having the pressure data on the gun it is fitted within, gives me all the data required for the SET POINT on the reg for that PCP.
If for instance said regulator has a 100 psi extreme drift but once cycling say doing FT duty stays inside a 50 psi drift .... and we know the gun in question sweet spots at lets say 1825 psi to 1900 psi .... and falls away in speed past this point will set the regulator up at @ 1825 which has it shoot very consistent, and if there is reg creep/drift we're still in the sweet spot and gun will continue to shoot perfectly with very low ES figures.
** The above is how I set up my MATCH guns personal or professionally.
Scott
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Another 8) 8) benefit to doing pressure testing for a PCP's is that one could SIMPLY ASSEMBLE A GUN WITH MIX & MATCH PARTS .... or Change the hammer weight, spring tension or pellet weight.
Start at lower pressure taking honestly 2-3 shots every 100 or more PSI and chart what the speed is doing, You either will see power come up with pressure, or fall away at some point.
All indicate something like for size of poppet and weight of hammer or spring is too little ... or valve is getting hit so friggen hard even high pressure won't prevent it from opening.
Point being within reason nearly any PCP will have a point in pressure that its power peaks, trick is to place this peak within a usable range of the guns pressure rating.
Used with the info in previous post ... one can sit back with a PCP and CHANGE hammer or spring specs, pellet weights etc ... and very quickly find AT WHAT PRESSURE the PCP peaks at using those components & setting. Want a shift in power ? play with the factors contributing and note what they do ;)
KEEP IN MIND we are speaking REGULATED and once you find the sweet spot pressure for the guns mechanical & pellet set up ... you set regulator accordingly.
It really is not rocket science once one wraps there mind around the basics fundamentals at play.
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Thanks Scott
I am trying to wrap my head around this info.......... a lot to learn, for me.
Tia,
Don
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Day 1 with a Lane reg on a gen 1 .177 mrod. Reg is set to 115 bar (asked for 16 ft lbs setting). Standard hammer spring and jefferson state lightweight hammer. With velocity port full open I had 950+ FPS so dialed it back to about 900. Striker full CCW and looking for the plateau, it was just falling off the plateau with hammer at full CCW. First full string from ~2900 got 85 shots within 4% ES averaging around 860 FPS. I probably could do a bit better with a slightly lower reg pressure and perhaps more control with a slightly weaker / shorter hammer spring. Thanks for the help, it's probably time to just shoot and work on that triggering.
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Scott, I would love to see you pressure test setup. What type of gauge are you using between your fill tank and AG?
Don - are you using a similar set-up as well. I'm not exactly sure of what such a config would look like (type of gauge needed, etc.).
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Hi everyone. I read this thread and there are a few things I'd like to ask about, if Bob and the rest of you don't mind answering after all this time has passed since the thread was started.
1. Perhaps I got it wrong, but my initial impression was this entire way of tuning refers to unregulated guns which are later fitted with a regulator. How about guns which are regulated out of the box? And their "preload on the hammer spring" is out of the box tuned to the lower regulated pressure?
2. Assuming that this entire process is recommended for guns manufactured with a regulator, I'd still like to ask about some of the details of the procedure and if I am understanding them right:
- So, you take your regulated gun and start increasing the tension on your hammer spring. Do you keep dialing in until you can dial no more? And if you do, do you think it is a good idea to make several shots to chrony your velocity with your tensioner dialed all the way in?
- After that, you start loosening little by little and keep testing the velocity with your chronograph until you notice the first drop in the muzzle velocity, is that correct? And as soon as you notice this first drop, you loosen no more, 'cause you've actually reached the so called "knee", the sweet spot (for the current regulator setting) and you leave it there?
Perhaps I am simplifying it too much; however, I'd like to know if that's what you guys are doing.
Thanks in advance for your responses.
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Yes, finding the knee point is where the hammer is being operated efficiently.
If not satisfied with the fps at this point then you have to look at the regulator setpoint
And possibly the other parts of the system, valve spring, hammer spring, hammer weight, plenum size etc
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This method applies to any regulated gun, either one converted from unregulated, or bought that way.... Increasing the hammer strike until the velocity plateaus, and adding more preload doesn't add any more velocity, is the only way to properly determine what you need to do to tune your gun.... Once you find the plateau velocity, reduce the preload until the velocity drops 3-5%.... That will be the "sweet spot" for the regulator setpoint you have.... If you are not happy with that velocity, then you need to change the regulator setpoint and start over with the process to determine the new plateau....
If you plateau is about 10% above your desired velocity, you can detune using just the preload to get the velocity you want.... However, when you drop that far (or more) below the plateau, when the tank pressure drops below the setpoint the velocity will INCREASE because the gun is now acting like an unregulated one (when below the setpoint pressure)....
Bob
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Bob, above all thanks for taking the time to reply.
"This method applies to any regulated gun, either one converted from unregulated, or bought that way..." - thanks, I thought so, just wanted to make sure.
"If you are not happy with that velocity, then you need to change the regulator setpoint and start over with the process to determine the new plateau..." - thanks, this I understand completely.
"If you plateau is about 10% above your desired velocity, you can detune using just the preload to get the velocity you want.... However, when you drop that far (or more) below the plateau, when the tank pressure drops below the setpoint the velocity will INCREASE because the gun is now acting like an unregulated one (when below the setpoint pressure)…" - thanks for this as well, I understand and I am not interested in shooting at velocities below my plateau. If I am not mistaken, the reason for this INCREASE is the reg remains "open" when the tank pressure drops below the reg setpoint, the hammer hits with the same force but the pressure it has to overcome is lower, and therefore the valve remains open for a slightly longer period of time and releases more air, even though at a lower pressure. Hence the increase in muzzle velocity, but of course this increase will be temporary before the pressure in the tank drops too much ;) Please correct me if I'm wrong.
What I am trying to do is wrap my head around how to apply in practice this method step by step.
So you buy a regulated gun (or fit a reg on an unregulated one), you take it out of the box and start adding more preload on the hammer spring. Not to increase velocity, but to find the plateau, I get it. So you add more preload on the hammer spring and chrony the gun every turn or so to see if the plateau is reached, correct?
Then, after you chronograph readings indicate you've reached the plateau, you reduce the preload until you calculate a drop of the plateau velocity by 3-5% - for instance, you find your plateau at 900 fps and you start reducing the preload until your velocity drops by 27 to 45 fps (rough estimates, of course). And then you've reached the sweet spot. Is that correct?
Thanks again.
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Alex, your reiteration of my statements is 100% correct.... What happens on the plateau is that once you reach it, releasing more air by using more preload is only blowing air out the muzzle after Elvis has left the building.... As you reduce the preload below the start of the plateau, you are closing the valve while the pellet is still in the barrel.... For most PCPs, closing the valve when the pellet is halfway down the barrel saves about half the air but only loses about 3% of the velocity.... Obviously, this is MUCH more efficient than operating on the plateau....
If in your example (plateau at 900 fps) you really needed to shoot at, say 950 fps, you would need to increase the regulator setpoint pressure enough to move the plateau up to at least 980 fps, find the preload required to reach that, and then detune 3% back to 950 fps.... You can get a pretty good idea of how much you would need to increase the pressure by calculating the difference in the plateau velocities, and then squaring that (to get the FPE), as follows....
980 / 900 = 1.0889 (ie nearly a 9% increase in velocity)…. That represents an increase in energy of (1.0889 x 1.0889) = 1.186 times.... Therefore, you would need to increase the setpoint pressure of the regulator by that same amount.... If your setpoint was 1200 psi when the plateau was 900 fps.... you would try a setpoint pressure of (1200 x 1.186) = 1423 psi.... So, if you increased the regulator setpoint to 1400-1500 psi you should be able to find an efficient tune at about 950 fps when you tune to 3-5% below the (now higher) plateau….
If you refer back to the graph in Reply #91 on the previous page, you can see what happens to the velocity curve as you reduce the preload.... Note what happens if you drop the velocity 10% or more below the plateau.... Below the setpoint, the gun shoots like an unregulated PCP (because it is, the regulator is wide open)….
Bob
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Bringing this one back from the other side. Been playing with a 12FPE tune on an HW100 and found the answer I was looking for here. I thought this one was stickied ?
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Very informative thread. I sure learned a lot. Thanks to everyone who has contributed to the learning process an to Bob especially for starting it with such viable information that everyone can benefit.
Peter
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Alex, your reiteration of my statements is 100% correct.... What happens on the plateau is that once you reach it, releasing more air by using more preload is only blowing air out the muzzle after Elvis has left the building.... As you reduce the preload below the start of the plateau, you are closing the valve while the pellet is still in the barrel.... For most PCPs, closing the valve when the pellet is halfway down the barrel saves about half the air but only loses about 3% of the velocity.... Obviously, this is MUCH more efficient than operating on the plateau....
If in your example (plateau at 900 fps) you really needed to shoot at, say 950 fps, you would need to increase the regulator setpoint pressure enough to move the plateau up to at least 980 fps, find the preload required to reach that, and then detune 3% back to 950 fps.... You can get a pretty good idea of how much you would need to increase the pressure by calculating the difference in the plateau velocities, and then squaring that (to get the FPE), as follows....
980 / 900 = 1.0889 (ie nearly a 9% increase in velocity)…. That represents an increase in energy of (1.0889 x 1.0889) = 1.186 times.... Therefore, you would need to increase the setpoint pressure of the regulator by that same amount.... If your setpoint was 1200 psi when the plateau was 900 fps.... you would try a setpoint pressure of (1200 x 1.186) = 1423 psi.... So, if you increased the regulator setpoint to 1400-1500 psi you should be able to find an efficient tune at about 950 fps when you tune to 3-5% below the (now higher) plateau….
If you refer back to the graph in Reply #91 on the previous page, you can see what happens to the velocity curve as you reduce the preload.... Note what happens if you drop the velocity 10% or more below the plateau.... Below the setpoint, the gun shoots like an unregulated PCP (because it is, the regulator is wide open)….
Bob
Thank you, Bob for sharing your knowledge so readily; and thanks Alex for your question as it clarified the tuning info for me considerably.
Bob, here is my question.
I'm planning on installing a Huma regulator in Disco 22.
My understanding is that when doing that the rifle's pressure gauge will register the regulator setting.
I find this useful as a reference; and would like to keep that function
However I would also like to know the fill pressure at all times.
What would be the best way to add a fill pressure gauge?
My thought is to add one at the fill fitting but imagine there are other methods as well
Will you advise, please, on the best method (including hardware) to accomplish the task
Thanks
and Merry Christmas /Happy Holidays to all
Ed
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Following
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I have seen it done with a high pressure "T" fitting.... Other than making a whole new front end with gauge and fill ports I don't know of another way....
Bob
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I have seen it done with a high pressure "T" fitting.... Other than making a whole new front end with gauge and fill ports I don't know of another way....
Bob
Thanks, Bob
Fittings almost in hand (ordered)
Is the assumption correct that added the gauge at the fill port will measure Fill Pressure; while the original gauge will measure Regulator Output Pressure?
Ed
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Correct....
Bob
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Thanks
Again!
Ed
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With time comes increased clarity and understanding (ie I'm always learning).... so I thought I would revisit this subject to add a chart that might help you understand what happens as you tune a regulated PCP with progressively less velocity than the plateau.... Here is an updated version of the chart in the first post of this thread....
The 3%, 5% and 10% below Plateau velocities are approximate only, but will give you an idea of what happens as you reduce the hammer strike, and hence the velocity, on a regulated PCP.... It will show you exactly why I like to tune 3-5% below that plateau.... because (at about 5% down) you get a few more usable shots below the setpoint before the velocity drops off.... or at the very least (at about 3% down) you save a lot of air compared to tuning up on the plateau, with very little loss of power.... The chart also shows what happens if you tune about 10% (or more) below the plateau.... Note that below the setpoint the velocity increases significantly.... and while operating in that realm gives you extremely good efficiency, for some applications (eg. Field Target, or in some countries where there is an FPE or velocity limit) that bump could put you over the limit....
Every gun is a bit different, and yours might produce a curve like the "5%" one above only 3% below the plateau, or it might be 7% below.... but to date those would be about the outside limits I have found to produce a tune that has a usable shot string (ie within a ~1% ES) extending slightly below the setpoint, which is the tune I prefer.... I hope this chart allows you to visualize what I have tried to confer in this thread....
Bob
Bob, I just love reading your write-ups with those nice crisp graphs. This crystallizes it in my mind a tuning process...
1) Fill one's hpa tank unregulated--shoot--recording the pressure and speed of each shot
2) Observe a roughly constant rate of decline in speed to a point where said rate of decrease will increase notably--probably good to use a moving average(MA)
3) Create Setpoint for regulator 3-5% below the pressure of the last shot prior to observed increasing rate of speed decrease.
4) Refill one's hpa tank regulated--shoot--recording the pressure and speed of each shot again
5) Observe a roughly constant speed with near zero rate of decline in speed to a point where said rate will increase or decrease substantially--also good to use a MA
6) When case of notable increase of speed above the MA, then slightly increase the setpoint and repeat
7) Repeat from (4) until no notable increase of speed above the MA is observed.
At that point if you like the speed, then you are at the sweet spot for speed and shot-count with your regulator and gun setup.
I realize there are so many variables that can be tweaked, and I have read many if not all your tuning tutorials/experiences in open up air flow etc. Assuming that I have my ports optimal--opened up as full as possible for gun/caliber; is there an outer loop on this set of tuning steps that identify when and how much to proceed into changing of springs for Hammer and Valve? I read folks on here doing such changes, and wondering outside trial-&-error if their is a systematic process similar to what outlined in this thread that identifies when those should be altered and the gun re-optimized for its new configuration?
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Not the process I would recommend....
1. shoot a shot string and graph, keeping track of the pressure, so that on the downslope of the bell-curve, when it gets to the velocity you want, you know the pressure....
2. Assuming you have a 1 cc per FPE plenum, increase the pressure about 5% above that (10% if you have a 1/2 cc per FPE plenum) and use that as your setpoint....
3.Shoot the regulated version, starting with same hammer preload you had unregulated, record the velocity of each shot, reducing the preload between shots.... You should see a plateau of the velocity for a while, then at some preload setting the velocity should start to drop.... You want to tune about 3-5% below the plateau velocity....
4. If you need a higher velocity, increase the setpoint and repeat.... If you want a lower velocity, reduce the setpoint....
An example.... You have an unregulated PCP that starting at 3000 psi the velocity is 850 fps.... It climbs to 900, and then starts to drop again as the pressure decreases.... You want a velocity of 850 fps, and when the pressure falls to that, it is 2000 psi.... Set your regulator to 2100 psi....
Fill your reservoir, original preload setting, the first couple of shots are 870 psi, so you know you are close.... Reduce the preload a turn at a time.... When you are out 4 turns, the velocity is still 865-870 fps, so you know that the plateau is 870.... At 5 turns out is it 850, and 6 turns 820, and 7 turns 780.... With a plateau of 870, the "sweet spot" is 3-5% below that, or 827-844 fps.... That will be somewhere between 5 and 6 turns out on the preload....
Set the preload at 5.5 turns out, refill the reservoir, and shoot a complete string.... If you are happy, then you are finished.... If you want more power, increase the setpoint....
Bob
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Thanks Bob...that's simple enough--much appreciated.
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Learned a lot reading just this thread alone.
I have been learning my Dreamline classic .177 these days. I have played with the reg pressure, TP wheel, and HST. My goal was to get lowest FPS (sub 10FPE) and lowest noise with consistency out of this rifle.
I recently tried to tune it with higher pressure and lower HST, which makes the gun tuned to the “downslope”. I was getting really low FPS (sub-600) and the noise was minimal (with pellet. dry fire is louder than lower setpoint). My understanding is that this makes the gun really quiet and very efficient, but shooting under setpoint will make FPS much higher. If you refill before reaching setpoint all the time, does it even matter? While the gun is tuned to the downslope, is it normal for the ES to be much higher? I thought Bob mentioned the FT shooters tune like this but wouldn’t their shot to shot consistency create an issue, besides the below setpoint FPF increases? Is it possible to tune to downslope yet with a minimal ES?
TIA.
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You are correct, if you tune on the downslope and refill above the setpoint, you will never see the velocity rise.... The problem with doing that at a FT match is what would happen if they tested your gun JUST before you were going to refill it.... and as it dropped below the setpoint it went over 12 (or 20) FPE.... you'd be out, even if it was never your intent to shoot it that way.... The same could occur if you were in Canada, tuned to under 500 fps, but on the downslope and they checked the velocity and shot it down below the setpoint.... and it went above 500 fps.... Now you have a firearm.... ::)
The wild swings in ES when shooting well down on the downslope are due to the way the valve reacts to even TINY differences in hammer strike.... The valve is operating in partial valve lock, so a little bit of stickiness on the hammer and it locks more, and the velocity drops a lot.... If your hammer strike is PERFECT, every time, your ES should stay small.... I have an anecdotal report by one shooter who tuned well below the plateau, and managed to lower the ES by running a VERY strong valve spring.... He was running more pressure, and a light hammer strike, to get an efficient and quiet tune, but the ES was terrible.... He installed a heavier valve spring, and had to of course increase the hammer strike, and the ES dropped.... So he fitted a valve spring that was so stiff he could not even push it open with his thumb.... He had to crank up the hammer strike, of course, because a large portion of the hammer strike was now required to overpower the strong valve spring.... However, this meant that tiny hammer friction variations were lost in the much greater hammer strike, and the ES dropped to very low levels....
As I said, this is ancedotal, from one report, and I haven't tested it myself.... However, it makes sense that it could work to tune on the downslope, fit a very heavy valve spring, and then increase the hammer strike to compensate for the heavy valve spring.... It seems to me to be worth a try.... ;)
Bob
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Bob,
thank you for that excellent post — really helpful for me to understand the intricacies of PCP tuning. 👍🏼
Matthias
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Yes thank you Bob for all the insights and confirmations. I currently have my Dreamline tuned to the knee (sub 12FPE) and call it a day. The wild inconsistency between shots when tuned to downslope wasn’t worth it for the lower power (sub 10FPE). It was fun exploring all the tuning capabilities though!
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Hello,
Thanks for this tutorial, it really helped me to adjust regulator pressure and hammer strike but I have one thing to say about it.
Like explained I have found the plateau (at a given reg pressure), the fps are even lower with the hammer spring fully compressed and then as I reduce preload, the speed increases until it decreases again. I did set the tension at those 3% less velocity than maximum on the downslope where the sweet spot is. But what happened is that with the regulator creep, the first shot is always lower in fps compared to the next ones that are good. What I did to reduce this issue is finally to set the HST to still be on the plateau but at the end of it where the fps just start to drop and with this, no more fps drop with the creep. With this I almost don't lose any more shots.
Now another question came to me. The plateau and sweet spot you're talking about is for a given pressure to achieve the wanted fps? Those aren't 3-5% less than the maximum the rifle is able to do all settings maxed out?
Thx
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If your velocity in a regulated PCP drops as you add hammer spring preload past a certain point, the hammer is bouncing off the back of the valve.... That is basically a design fault, but if it is occurring then you should consider the plateau velocity to be the maximum velocity you can get at your setpoint pressure (before the hammer crashes into the valve).... Then tune to 3-5% below that velocity....
If you tune that way, and you are experiencing a lower velocity on the first shot, you must have a REALLY horrible regulator, as even 100 psi either way from the setpoint should not cause enough velocity change to even marginally affect the POI....
Bob
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Thanks Bob,
I've whitnessed it on FX Wildcat, same on 22 and 25 cal. Looks like how you say, the valve is bouncing on the spring on the other side of its travel. It happens especially with a lower reg pressure in the 125-130b range. I'm able to reduce this pressure because I've installed the Huma plenum XL but its in combination with the FX AMP regulator which works way better for me than the Huma that was delivered with it (it is a second hand WC). I've already opened the Huma but saw nothing special and for the moment I don't have planed to change the o-rings on it since the AMP is sufficient. Strangely with both regs I've always a plenum with a pressure of 10-15b lower than the tank after its off-reg and the gauges are correct.
Concerning the creep. The first shot is recorded at about 915fps and all the other shots are around 930 with +/- 6 fps change. Setting the HST a bit more in the plateau brought the 1st shot at the same level as the others.
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Makes perfect sense.... Closer to the plateau uses a bit more air, but reduces the shot to shot variation, in most regulated PCPs.... You may be experiencing some sort of hammer, or valve, stiction after the gun sits for a while.... If it is occurring only on the first shot after a refill, that could be the regulator, and may be very hard to eliminate.... If you shoot below the setpoint, the regulator is open when you start your refill, and the plenum side may be getting a bit of extra pressure before the regulator closes, hence the low velocity on the first shot.... Stopping your shots before the setpoint should eliminate it, if that is the problem....
Bob
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I thought I should probably add the latest version of the chart showing the effects of various ways to tune a regulated PCP....
(https://hosting.photobucket.com/albums/oo221/rsterne/PCP Internal Ballistics/.highres/Regulator Tunes Revised_zpstv4nytay.jpg?width=1920&height=1080&fit=bounds) (https://app.photobucket.com/u/rsterne/a/59674f5e-e0e0-494c-b053-58726736f031/p/388ef530-a235-4cdf-aa4d-fb0db2b3b25d)
You will notice that the grey line (tuning on the downslope) shows the shot-to-shot variation in velocity often experienced with this type of tune.... Any small variations in hammer strike are amplified because the valve is barely opening.... With this type of tune, the gun is using tiny "sips" of air at higher than the required pressure.... It is very efficient, but prone to this phenomenon....
Bob
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I thought I should probably add the latest version of the chart showing the effects of various ways to tune a regulated PCP....
(https://hosting.photobucket.com/albums/oo221/rsterne/PCP Internal Ballistics/.highres/Regulator Tunes Revised_zpstv4nytay.jpg?width=1920&height=1080&fit=bounds) (https://app.photobucket.com/u/rsterne/a/59674f5e-e0e0-494c-b053-58726736f031/p/388ef530-a235-4cdf-aa4d-fb0db2b3b25d)
You will notice that the grey line (tuning on the downslope) shows the shot-to-shot variation in velocity often experienced with this type of tune.... Any small variations in hammer strike are amplified because the valve is barely opening.... With this type of tune, the gun is using tiny "sips" of air at higher than the required pressure.... It is very efficient, but prone to this phenomenon....
Bob
I counter the shot-to-shot variance in lower power tunes by utilizing a valve lift limiter built into my hammer that can be tuned externally with an allen wrench. Works well for tunes at 3-5% and 10% below the plateau, although you still get the rise in fps once you're off the regulator with lower power tunes, its worth those extra shots while on regulator if the lower power suffices.
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And this grey colored tune is also very quiet, right?
Matthias
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Yes, it is quiet.... Matt is obviously using excess hammer strike, and then tuning the lift/dwell by limiting the travel of the valve stem to avoid the shot-to-shot variation.... I have not done that, but it should work fine.... I do not understand why you should get the velocity rise below the setpoint if you are limiting the lift, but if Matt says it happens, I would believe him.... I just don't know why it would occur.... Unregulated PCPs that have travel limiters, like the Korean guns, have dropping velocity at lower power tunes as the pressure drops....
Bob
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About the soft report of being adjusted well under the knee...I'll never forget a few years back when a buddy asked me to come over to his suburban yard one Saturday morning and take out some gray squirrels. He told me the shots would be a max of 30-35 yards so the night before I took a regulated .22 cal at 30fpe and began dialing back the hammer spring tension to see how it would do at about half power and switch to the lightweight JSB RS (13.4gr) to keep the trajectory fairly flat.
At the time I had no idea what to expect but I remember pulling the trigger and hearing sort of a pip of the hammer gently tapping the valve stem. I thought, oh I went too far and looked down at the chronograph expecting to see 300fps. No, it was 700fps. The velocity was jumping around but it was keeping all the pellets inside a dime at 25 yards so that's where I left it.
Well that was just the ticket. We had 3 down within minutes of arriving, the report so soft they didn't perceive a threat. It went on to do 6 for 6 that day. So yeah for a scenario like that or for something like basement target practice, it makes for a very pleasant shooting experience.
https://www.gatewaytoairguns.org/GTA/index.php?topic=78577 (https://www.gatewaytoairguns.org/GTA/index.php?topic=78577)