Author Topic: Tuning a Regulated PCP  (Read 6123 times)

rsterne

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Re: Tuning a Regulated PCP
« Reply #15 on: November 19, 2017, 04:35:06 PM »
As you lower the pressure the plateau velocity will lower as well.... Only if you are below the knee of the curve will the velocity increase with reduced pressure.... If that happens then you can assume you are somewhere on the downslope.... ie more hammer strike would increase velocity....

Bob
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charmin99

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Re: Tuning a Regulated PCP
« Reply #16 on: November 23, 2017, 03:55:26 PM »
Hello Bob,

Last question..

OK, so I have found the knee by trying various preload and dwell settings on the hammer and spring changing (costly..) and some calculation, also opened up the transfer port to optimise available setpoint pressure.

I have plotted it out and as your example it is pretty flat with a 2ft/sec variation with an amazing flat shot string of 80 then quickly falling off below at what would be the setpoint pressure.
Set point 125 bar, cylinder fill 205 bar.

The original un-regulated setup gave quite a power curve with only 38 useable shots and chronoed at 11.6 Ft/lb - 786 Ft/sec with JSB Exact 15.44

Now I have 11.0 Ft/lb 765 Ft/sec with same pellets but 80 string shots flat as a pancake...

The question, as the variation is now very good and more likely due to chrono variation I am quite happy with the result as I shoot HFT I want repeatability, however if I wanted to increase the velocity up, to say 11.6Ft/lb (785Ft/sec) and re-adjust the setpoint up, now the balance between the firing valve, striker and transfer port are set, if I just adjust the setpoint up marginally to the 11.6Ft/lb I guess I will loose a few flat shot, loose  some of the efficiency and sacrifice that for a bit higher power, is that adjustment to the setpoint now going to be a linear adjustment or close to it or would I have to start all again, which I couldnt face to be honest.

Or as you say, "enjoy what you've got.."

Thanks

Malc

  • Portsmouth, UK

rsterne

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Re: Tuning a Regulated PCP
« Reply #17 on: November 23, 2017, 04:56:09 PM »
So is the 765 fps the fastest you can get at your current setpoint, regardless of hammer preload?.... If that is the case, then yes, you need to increase the setpoint slightly to get closer to 12 FPE.... The increase in FPE should, in theory, be proportional to pressure, so if you are at 125 bar now, then 130 bar should give 11.44 FPE and 135 bar about 11.88 FPE.... Yes, you will lose some shots, both because the efficiency will be slightly less (more power) and also you will have less pressure drop from full to setpoint.... Currently you have 205-125 = 80 bar of air usable, with 135 bar you would only have 205-135 = 70 bar.... At best, your shot count should drop to 80 x 70 / 80 = 70 shots.... but probably more like 65 shots at 11.9 FPE, maybe a bit less....

or, as you say, be happy with what you have now....

Bob
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charmin99

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Re: Tuning a Regulated PCP
« Reply #18 on: November 23, 2017, 05:37:49 PM »
Thanks Bob,

Just wanted to check my thinking was correct and yes the 765 fps is the fastest.

I will have a think about it after shooting off a few more pellets (200 so far for just for this..) and see how it behaves, scope and everything set up for current setting now and as you well know this is an iterative job and personally I find you've had enough fiddling after a while... haha.



I can well live with 60 ish shots but as I said the flatness is key for me, just that over here in the UK, wind and rain on a Sunday morning shooting you can do with that last few fps...

If I do it I will let you know how it went, but can I just say many thanks, I have learnt an awful lot, yours is probably the best and most concise, relevant info I have found to date.

Many thanks

Cheers
 
 Malc
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Josparky

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Re: Tuning a Regulated PCP
« Reply #19 on: April 12, 2018, 03:09:17 PM »
Bob thank for such a very informative post. I have read through it many times and thought I understood what to do but have run in to a problem. I seem to be stuck on the plateau I think trying to get to the knee so all shots are flat. I have a gen 2 Maruader with a huma regulator I just installed. I set the gun I thought before I put the regulator in but apparently something is still wrong. I have the Hammer spring set to 4 turns in the Transfer Port screw out 4 turns and locked down and the Hammer Strike the full shortest I could set it from the book to 12 Turns in. Here is what I get.

Just installed a Huma Regulator in a stock gen 2 Marauder 177. Have the TP screw set to 4 turns out, the HS 4 turns in and the HT 12 turns in here is the string I got out of it below. It seems to drop off slowly all the way to 1450 where I have the regulator set at. What can I do to get it to stay more the same. Note I will be keeping all the stock parts. Just wanted to add the regulator. It was at 1450 at the 90th shot. Any help would be appreciated. Thanks

Ok guys here is what I got on 3rd string after regulator started settling in a little and I made some adjustments. I run the HT in 12 turns that is when I started saving air and the HS in 4. It was at 1450 at shot 90 which is where I set the regulator at. Seems to be dropping slightly throughout the shot string. Is there a way to make it stay the same throughout the shot string???

Created: 04-11-2018 04:20:22 PM
Description: testing reg 3 4 spring 12 throw
Notes 1:
Notes 2:
Distance to Chrono (FT): 0.00
Ballistic Coefficient: 1.000
Bullet Weight (gr): 0.000
Altitude (FT): 0.0
Temp: 70 °F
BP: 30.03 inHG
Shots
# FPS FT-LBS PF
93 848 0.00 0.00
92 859 0.00 0.00
91 862 0.00 0.00
90 861 0.00 0.00
89 858 0.00 0.00
88 856 0.00 0.00
87 861 0.00 0.00
86 859 0.00 0.00
85 866 0.00 0.00
84 861 0.00 0.00
83 868 0.00 0.00
82 ERROR 10
81 871 0.00 0.00
80 872 0.00 0.00
79 862 0.00 0.00
78 858 0.00 0.00
77 863 0.00 0.00
76 865 0.00 0.00
75 856 0.00 0.00
74 867 0.00 0.00
73 859 0.00 0.00
72 863 0.00 0.00
71 867 0.00 0.00
70 865 0.00 0.00
69 865 0.00 0.00
68 863 0.00 0.00
67 871 0.00 0.00
66 876 0.00 0.00
65 873 0.00 0.00
64 872 0.00 0.00
63 870 0.00 0.00
62 863 0.00 0.00
61 872 0.00 0.00
60 867 0.00 0.00
59 869 0.00 0.00
58 868 0.00 0.00
57 866 0.00 0.00
56 870 0.00 0.00
55 868 0.00 0.00
54 863 0.00 0.00
53 870 0.00 0.00
52 869 0.00 0.00
51 872 0.00 0.00
50 870 0.00 0.00
49 872 0.00 0.00
48 872 0.00 0.00
47 868 0.00 0.00
46 869 0.00 0.00
45 872 0.00 0.00
44 876 0.00 0.00
43 872 0.00 0.00
42 880 0.00 0.00
41 878 0.00 0.00
40 878 0.00 0.00
39 875 0.00 0.00
38 881 0.00 0.00
37 878 0.00 0.00
36 880 0.00 0.00
35 879 0.00 0.00
34 878 0.00 0.00
33 872 0.00 0.00
32 884 0.00 0.00
31 880 0.00 0.00
30 880 0.00 0.00
29 886 0.00 0.00
28 873 0.00 0.00
27 881 0.00 0.00
26 885 0.00 0.00
25 884 0.00 0.00
24 886 0.00 0.00
23 887 0.00 0.00
22 889 0.00 0.00
21 877 0.00 0.00
20 885 0.00 0.00
19 887 0.00 0.00
18 881 0.00 0.00
17 893 0.00 0.00
16 885 0.00 0.00
15 887 0.00 0.00
14 887 0.00 0.00
13 888 0.00 0.00
12 890 0.00 0.00
11 884 0.00 0.00
10 883 0.00 0.00
9 884 0.00 0.00
8 886 0.00 0.00
7 890 0.00 0.00
6 890 0.00 0.00
5 892 0.00 0.00
4 888 0.00 0.00
3 880 0.00 0.00
2 889 0.00 0.00
1 884 0.00 0.00
Average: 874.01
StdDev: 10.24
Min: 848
Max: 893
Spread: 45
True MV: 874.01
Shots/sec: 0.03
Group Size (IN): 0.00

Now I tried turning the Hammer Spring out to reduce the spring tension and it is lowering the velocity but still drops over the total string what can I do to get it as flat as possible all I need to get is 60 good shots so I don't care about loosing some shots I just want it on the knee as you show in the drawing. Thanks for any help you can provide.
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rsterne

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Re: Tuning a Regulated PCP
« Reply #20 on: April 12, 2018, 05:52:42 PM »
I never use hammer travel to tune, so pretty hard for me to comment on a tune where you have reduced the travel by 12 turns (about half the available travel).... The problem with the way the MRod is designed is that as you decrease the hammer travel, you increase the hammer spring preload, so you have two adjustments fighting each other....

What happens if you use the hammer travel you have now, and start with the preload at maximum, shoot one shot, reduce the preload a turn, shoot another shot, etc.etc..... That is how you determine where the knee is.... If you are stuck at maximum velocity all the way to minimum preload, then you need a lighter or shorter hammer spring....

Bob
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Josparky

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Re: Tuning a Regulated PCP
« Reply #21 on: April 12, 2018, 06:02:23 PM »
Thanks for the reply if I increase the hammer spring now it raises the fps if I lower the hammer spring it decreases the fps.
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rsterne

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Re: Tuning a Regulated PCP
« Reply #22 on: April 12, 2018, 06:13:48 PM »
Then you are not on the plateau, you are either on the downslope or the knee.... What is the maximum velocity you can achieve at the current 1450 psi setpoint?.... What velocity would be your ideal goal?....

Bob
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Josparky

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Re: Tuning a Regulated PCP
« Reply #23 on: April 12, 2018, 06:41:30 PM »
My ideal goal is to stay around 875 to 880 throughout the whole string right now when it drops off the regulator it starts dropping as you can see from the string above. So if my studying is right it should be in the pleatue if I spelled that right lol. But when I start dropping the hammer spring it starts dropping the fps. Now I can lower the hammer throw and get that fps back up but only a few turns. I will loose some shots but that's ok with me if that's what I need to do. I did before dark  let the hammer spring out one turn so it is at 3 in now and I turned the hammer throw out one turn also now at 11 to get the fps back up to around 880 and it seemed consistent still but I only had time to take a few shots after that didn't get a whole string in but the shots where around 875 to 885. I know the regulator needs to settle in from what I am told it may take around 300 shots for that. I have run around 150 to 200 through it so far.
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rsterne

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Re: Tuning a Regulated PCP
« Reply #24 on: April 12, 2018, 08:19:05 PM »
Josparky, don't take this personally, it is intended to help ALL those who continually ask me the same questions....

If you don't know what the maximum velocity is, you don't know where you are in relation to the plateau.... This is the most common problem people have when trying to tune a PCP, they don't take the time and the few pellets to find out where they are at.... THE FIRST STEP IS TO DETERMINE THE MAXIMUM (PLATEAU) VELOCITY, WHERE THE KNEE IS, AND WHERE THE DOWNSLOPE STARTS.... I am getting frustrated with people asking for help, and not taking this simple first step.... PLEASE, EVERYONE, DO THIS FIRST, I CAN'T HELP YOU IF YOU WON'T HELP YOURSELVES....

1.  Crank the preload to the maximum, shoot a shot, record it....
2.  Reduce the preload a turn, and repeat....
3.  Continue until the velocity is falling a lot
(like 100 fps per turn), or it is way below what you would ever want....
4.  Draw a simple graph like this, you don't need to use a spreadsheet, graph paper will work just fine.... (two pellet weights are shown)....



5. Determine at what preload the plateau starts (-3 T for the 34 gr., -4 T for the 25 gr. above).... you will never need more preload than that....
6. Determine what the velocity is on that plateau (this is the maximum at your setpoint pressure, 1060 for the 25 gr., 970 for the 34 gr.)....
7. The downslope is where the velocity is dropping rapidly, maybe 100 fps per turn (850 @ -5T for the 34 gr., 900 @ -5.8 T for the 25 gr.)....
8. The knee of the curve is the part between the plateau and the downslope, where the line is the most curved.... THAT is the only area you want to tune within....
9. If the velocity on the knee is higher than your goal, reduce the setpoint pressure....
10. If the velocity on the knee is lower than your goal, increase the setpoint pressure....

The best tune, IMO, is usually between 3-5% below the plateau velocity.... and NEVER more than 10% below it....
You can tune lower than that, but the velocity will INCREASE below the setpoint, and often the ES is large, with a high shot-to-shot variation, because the valve is operating in partial valve lock.... You need to reduce the setpoint pressure to get back on the knee of the (now lower) curve.... If the plateau is lower than your required velocity, you need to raise the setpoint and start over.... Each time you change the setpoint, do another curve, DON'T GUESS....

Using the above curves, I tuned for the 34 gr. at 940 fps at -4 turns.... That is 3% below the plateau.... I could have tuned it for more shots at 900 fps (-4.5 turns), which is 7% below the plateau, but much lower than that I would reduce the setpoint.... This 1900 psi setpoint is ALMOST TOO HIGH for the 25 gr. pellets.... To drop the velocity to 950 fps, where I would want it, I would be operating nearly on the downslope, and about 10% below the plateau.... The gun would be very efficient tuned like that.... but the ES would be increasing, and once the pressure dropped below the setpoint, the velocity would bump up more than a percent, likely 2-3%.... I would obtain a better tune by reducing the setpoint to about 1700 psi to drop the plateau velocity to 1000 fps or just below, and then tune on the knee, 3-5% below that (now lower) plateau, to get my desired 950 fps....

The greatest stability in shot-to-shot velocity, and the lowest ES.... plus the minimum effect from any regulator creep.... will occur when you tune to the knee of the curve.... It is like shooting an unregulated gun right near the top of the bell-curve, where the ES is the smallest, and slight differences in hammer strike or pressure make almost no difference to the velocity.... The closer you are to the plateau velocity, the more power but the lower the efficiency and shot count.... The closer you are to the downslope, the less power but the higher the efficiency and shot count BUT watch out for increase ES and the velocity INCREASING below the setpoint....

Bob
« Last Edit: April 12, 2018, 09:58:45 PM by rsterne »
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Josparky

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Re: Tuning a Regulated PCP
« Reply #25 on: April 12, 2018, 08:47:19 PM »
Thanks Bob again for your help and reply. I take nothing personal in this life anymore my friend. We are not all as smart as some of you and we do really appreciate the time you take to help us. I will take the time to do exactly what you said this last description I am sure will help others to understand what they need to do as well. This does add some lite to how to get to where we need to be. I can only think of one more thing to help me and others out so you are not bothered with us as much. Can you add to that last post a simple explanation of if we never get to the plateau or vise versa cant get off the plateau which way we would need to move the setting pressure on the regulator to find it. I hope you understand what I am asking. Then I think most could figure this out a lot easier without having to ask anymore questions. I hope I have made since with my last question. If it is already answered in here please forgive my ignorance in not seeing it. AGAIN I REALLY REALLY REALLY DO APPRECIATE YOUR WILLINGNESS TO SHARE YOUR KNOWLEDGE WITH THE COMMUNITY NOT EVERYONE IS WILLING TO DO THAT.
« Last Edit: April 12, 2018, 08:48:56 PM by Josparky »
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rsterne

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Re: Tuning a Regulated PCP
« Reply #26 on: April 12, 2018, 09:41:26 PM »
Since in almost all cases when a regulator is installed in a PCP, you are reducing the pressure at the valve, there should never be a situation where you can't get to the plateau, assuming you had any reasonable bell-curve in the unregulated version.... More likely, you may not be able to tune the preload LOW enough to get below the plateau.... However, here is that information....

If you are stuck on the plateau and no matter what you do you can't reduce the velocity, you need to either shorten the hammer spring or replace it with a weaker one, and/or fit a lighter hammer.... Alternately, if you want more velocity, you can increase the setpoint pressure....

If you are on the downslope and cannot reach the plateau (and hence are not sure where the knee is), you need a stronger hammer spring, or a spacer to increase the preload (if the spring isn't at coil bind), or you can try a heavier hammer.... Alternately, if you have too much velocity, you can decrease the setpoint pressure....


Bob
« Last Edit: April 12, 2018, 09:53:04 PM by rsterne »
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Motorhead

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Re: Tuning a Regulated PCP
« Reply #27 on: April 13, 2018, 08:21:36 AM »
I had strongly suggested a lighter hammer and higher set point in another thread where the same inquire was made ....
sadly attempting to stay with 100% oem parts with a regulator added has been proven time & time again to fall way short of ideal or able to do what a gun can that has been altered to best utilize regulation modifications.
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