How much effect of a consistent regulator on accuracy?

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mubhaur

mubhaur

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Nov 8, 2015
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The Edgun digital guage helped me to read the regulator reading accurately for the first time. 

I witness that normally the regulators are inconsistent in around 4 bars to 5 bars and after leaving the gun for more time there may come the variation of a bit more bars.

I did all this experiment with FX Impact AMP regulator. 

Without digital guage I could not find it out.

Now I want to discuss and know that for extreme long range accuracy how consistent the regulator should be in terms of shot to shot bars and after a few minutes. 



I understand that the valving system of the pcp itself regulates the fps. 

I want to discuss that if regulated pressure varies between 5 bars, is it adequate for extreme long range accuracy?

Or the regulator must be between 1 or 2 bars?

I understand that this aspect of regulator inconsistency needs to be discussed in detail with respect to long range accuracy. 

Regards, 

Umair Bhaur 
 
Umair, I don't think you will find your answer here, as most of us have no way of knowing the variation in our regulators. The rifles that have reg gauges are not sufficiently accurate for this purpose. I believe the only practical approach for most of us is to work with a chrono as we tune. If accuracy is poor, and velocity is erratic, the reg could be the issue, or one of several. I've had rifles with velocity ES at a level I thought poor, but shot very well. It will for sure affect accuracy, beginning at a given distance. The question then, is your shooting distance within the the capability of your rifle, part of which is the reg? For example, I improved the accuracy of a rifle by changing regs, and velocity ES was much smaller. But, I have no idea of the pressure consistency in either regulator. 
 
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If you're talking about groups, anything over a few bars screws up my groups from 100y and beyond. I was trying to eliminate variables a few weeks ago while trying to reduce spread / deviation, and I was filming my regulator manometer while target shooting across both my Caldwell and LabRadar. I was using 27gr NSA slugs for the test, and all the slugs were identical in side weight and shape. I also wanted to see how fast or slow the reg took to depressurize between shots, and filming this was harder than you'd think (part of the reason I bought a small shooting vise).

While I cannot be certain about the variation of force in my spring and hammer, the one metric that was consistent with velocity drops (and bumps) affecting the accuracy of my groups was reg pressure. 
 
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As RJ mentioned, the single best thing you can do is set up the tune so it is least sensitive to pressure variations. Crank up the HST until the velocity no longer increases, and then dial it back until the velocity falls to about 97% of that maximum. When set up in this manner, it is analagous to being at the peak of the bell curve of a traditional unregulated PCP:



The region represented by the box (dotted line) is where the velocity is quite stable despite spanning a pressure range of 2600psi down to 1900psi, or a change of 700psi / 48 bar. So for example, you could take this rifle and regulate it at ~2250psi (the midpoint of that pressure range) and the regulator could vary 20 bar in either direction and have a negligible effect.

Granted, most regulated PCPs will not be so well balanced for whatever velocity we happen to pick as our goal. This balance is a combination of pressure, porting, hammer weight, hammer stroke, hammer spring tension, and the valve return spring. So if you really want to make a particular gun as agnostic as possible to pressure variations, you can start by tuning it as an unregulated rifle and manipulate those parameters for the broadest possible useful pressure range.

But unless something is wildly out of whack, it's probably not worth it. Regulators afford us the luxury of being a bit sloppy. They allow us to achieve good results even when things aren't optimally balanced. And that's okay because hopefully we never have a regulator that is as erratic as the example I used. So for the most part we can take the convenient shortcut of adjusting the HST to 97% of maximum velocity and promptly enjoy an extreme spread that is as good as can be expected when taking all the other factors into consideration...things such as variations within the pellets themselves and the repeatability of the hammer strike due to friction, subtle sear drag, etc.
 
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That’s great info there Jason, thank you!

question...

How is 97% THE number? Why not 92% or any other number?

Another question...

If I am targeting a specific velocity, I am assuming that I need to adjust the regulated pressure (regulator) up or down depending on where I want that velocity (97% max) to be?

^^^^^^^

Is that for maximum efficiency? (Air usage per shot for velocity of projectile generated)



Say max velocity is 920fps and I’m targeting 850fps, why not just dial the HST down until I hit my desired speed?



I hope those questions make sense. I’m just trying to learn here, thanks!
 
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The 97% is not a precise number. If something is way out of balance, it may be worthwhile to play around with the regulator setpoint and see how the gun responds, or better still, see how it behaves in unregulated form to establish a baseline. But it works well in most cases.

If you want to tune to a specific velocity, yes it's a good idea to adjust the regulator's setpoint so that the 97% figure gives you the velocity you want*. Not so much for efficiency but for consistency (holding a tight ES). Granted it will be much more efficient than going for peak velocity but not as efficient as backing way down, which brings us to your other question.

If your max velocity is 920fps and your goal is 850fps, that works out to about 92%. That is not unreasonable and it may be that the gun will hold a tight ES as long as it's on the regulator. However it will be more sensitive to a velocity loss if the regulator creeps and it will also experience an increase in velocity as the pressure falls below the regulator's setpoint. 

The mechanics at play are easier to understand if we look at a more extreme example. Let's say the max velocity is 900fps and the goal is 700fps. To downtune that much by simply backing off the hammer spring tension, what is happening is the hammer is barely knocking the valve open. Really low lift and very short dwell. The valve is open for a teeny tiny fraction of the time the pellet is in the barrel and accelerating. Tiny variations in friction lead to wild velocity swings. If we kept going down further, we would eventually reach complete valve lock.



With that said, this type of tune is very efficient if you can tolerate the extreme spread. Very efficient also means very quiet. A modest de-tune can be quite useful for back yard plinking or discreet pest removal in a suburban setting. Just not something you'd generally want to do for 50+ yard duty. 

* The other way to shift the velocity up or down is to change the porting (the cross-sectional area of the path the air follows). You can do one or the other or a combination of both. For example when adding a regulator to a rifle that was designed as an unregulated rifle, it's pretty typical to increase the porting. That way it can produce as much (or more) energy than it previously did, despite now operating at a lower pressure.
 
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Let me say something controversial. A regulator does not, in itself, impact accuracy at all. A regulator reduces the variability of air pressure, but does not completely eliminate it. No regulator is perfect. 

Working with Tom Holland, I experimented with regulating my Marauder. I managed to reduce FPS extreme spread to about 4 fps, but that took washing, lubing, and weighing pellets to 1/10 of a grain and shooting pellets only at that exact weight. As for accuracy, I'm still playing with the valve settings to reduce a 50 yard group size. Just because I reduced the FPS extreme spread doesn't give accuracy. Crosman Premier Domes were giving about a 3 inch group at 50 yards. JSB 18.13's were much tighter and I believe the 15.89's will be even tighter.

Even if you had a perfect regulator, accuracy may be terrible if you choose the wrong pellet The consistency of the regulator is only one of at least 6 factors if not more (velocity, pellet weight, pellet BC, distance to target, barrel condition, barrel harmonics, etc.) in accuracy, so, accuracy is a game of balancing all factors. 

The only way to prove that a 5 bar variation in regulator pressure would impact accuracy would be to eliminate all factors except the regulator and shoot groups. I personally don't have the ability to do that, but consider 5 bar insignificant in the grand design of the gun.


 
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The 97% is not a precise number. If something is way out of balance, it may be worthwhile to play around with the regulator setpoint and see how the gun responds, or better still, see how it behaves in unregulated form to establish a baseline. But it works well in most cases.

If you want to tune to a specific velocity, yes it's a good idea to adjust the regulator's setpoint so that the 97% figure gives you the velocity you want*. Not so much for efficiency but for consistency (holding a tight ES). Granted it will be much more efficient than going for peak velocity but not as efficient as backing way down, which brings us to your other question.

If your max velocity is 920fps and your goal is 850fps, that works out to about 92%. That is not unreasonable and it may be that the gun will hold a tight ES as long as it's on the regulator. However it will be more sensitive to a velocity loss if the regulator creeps and it will also experience an increase in velocity as the pressure falls below the regulator's setpoint. 

The mechanics at play are easier to understand if we look at a more extreme example. Let's say the max velocity is 900fps and the goal is 700fps. To downtune that much by simply backing off the hammer spring tension, what is happening is the hammer is barely knocking the valve open. Really low lift and very short dwell. The valve is open for a teeny tiny fraction of the time the pellet is in the barrel and accelerating. Tiny variations in friction lead to wild velocity swings. If we kept going down further, we would eventually reach complete valve lock.



With that said, this type of tune is very efficient if you can tolerate the extreme spread. Very efficient also means very quiet. A modest de-tune can be quite useful for back yard plinking or discreet pest removal in a suburban setting. Just not something you'd generally want to do for 50+ yard duty. 

* The other way to shift the velocity up or down is to change the porting (the cross-sectional area of the path the air follows). You can do one or the other or a combination of both. For example when adding a regulator to a rifle that was designed as an unregulated rifle, it's pretty typical to increase the porting. That way it can produce as much (or more) energy than it previously did, despite now operating at a lower pressure.
Click to expand...

Thank you once again Jason! Very clearly explained. Even I understood it. Ha ha!

Here is more on pcp tuning. Thanks to another member for giving the heads up where to search for the info. There may be some interest there for some of you.

https://hardairmagazine.com/category/ham-columns/airgun-technical/
 
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I have had my fx impact mk2 for about 2 month, and have send it back for repair but it did not help. My poi shift in groups ( 5 shot group in center then 5 shot to the left and so on) i havent even been able to sight it in yet, then i found out that it is the regulator that is bad and it creaps but you could not see it on the new and improved gauges.it also had a ES of 63fps, when it have shot a few mags it goes down to around 30-40fps in ES... I have orderd a huma regulator, that should do the job..

my dealer claimes that it was good when they send it back and 1” groups is accepteble for a fx impact on 25 y ( wtf)..



my barrel on this one is very sensible to speed so it dont take much to shift poi. 

Iam at the point where i am considering selling my impact an go with a daystate becouse this gun will never be ass good as i wanted to be, i have seen First hand that there is a huge differents from impact to impact some shots like a lazer and some you just have to work on constantly to get it to shot dicently.




 
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