Reg Pressure Effects on Pellet Stability

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mtnGhost

mtnGhost

Member
Dec 15, 2018
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Defected from the PNW, United States
I was going to long wind this, but let me TL;DR it for brevity as best that I can. I have a Leshiy + Huma standard reg, that I wanted to keep high power tuned for .25 JSBs and long range shooting with my .22 barrel.

Say I have a target pellet speed of 900fps for the .22 pellets. I can achieve the speed with both very high reg settings and low HST and with lower reg settings with higher HST.

Can high regulator pressures negatively affect pellet stability for a given speed vs. a softer Pressure with a lower reg setting?

Im beginning to think that even though the chrono will show the same speeds with both tubes, the high pressure / shorter valve sweep time might just be too much for light pellets out of my barrel.

Could it be possible that a 15-30 bar softer pressure would invoke better pellet stability?
 
In the recent post I made re-history of ag accuracy I showed groups shot by Lampies Lamprecht in RSA .( See the pic in my post down the page)

In an oblique way part of the answer to your question may be addressed. Note the bar fill readings in what I think (but will stand correction if wrong) for his TM was running unregulated. I have run mine unregulated in .177 to get up to as high as 28 fpe to shoot certain pellets with great accuracy. Lampies was shooting his as a .22 with 18.1 gr JSBs.

Note he used two different fill pressures for the two groups 180 and 160 bar.

It is obvious that the pellets were not damaged in shooting those wonderful groups. He has plenty more of near same quality.

Of course if one of your options was wasting the air charge at muzzle, some upset could result but I do not think that is what you are concerned about.

Kind regards, Harry.
 
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This is just theory, my 2 cents. / ideas

Normal diabolos are not made for too much speed, someone told me once 950 max (a lot of experience on his side) more than that they got destabilize , and for accuracy between 800-900 fps (in old ones not redesigned)

On the other hand more reg pressure usually mean more vibration due the hammer striking with more force, so less accuracy, so is key to keep vibration at minimum , so while pressure itself on the reg might nor affect (as long no air is wasted) the hammer might as consequence, and some AG might be better on that than others. (reducing vibe)
 
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My style of tuning has always produced good accuracy.

My belief is that there is only one ideal hammer spring tension for a given reg pressure.

So I will decide on a target velocity first. Then start at a low reg pressure and tweak the hammer spring for max velocity at that pressure. 

If my target velocity is not reached, I increase pressure by 5 bar and try again. I repeat this procedure until I get my target velocity. 

Whatever reg pressure that ends up being is what I stick with. Basically what that gets me is the lowest reg pressure with a level of hammer spring tension that suits that pressure.
 
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@Bob_O, I had this realization as well. I can almost always figure out what HST is best by listening for the change in sound too, usually most pronounced when I'm testing "backwards" over my chrono, where I'll start with a higher HST for a given Pressure and work my way down. When the sound tightens up, the chrono strings usually have the narrowest extreme spread.

@Yrrah yes, that was a great read too. There was also some eloquent points underscored in that thread that translated to the variables in obtaining near perfect groups. I can no longer discount pellet weight with this particular problem, and I'm reading into issues that others have published about the weight variations with the 15.89gr JSBs. I never intended to go as far as weighing, washing, and lubricating my pellets when I got back into airguns, but I do thoroughly enjoy shooting long range - and given the physical limitations imposed with airguns, I may not have a problem with washing and weighing them to achieve tighter groups.

@edosan - they certainly get loopy at speeds above that threshold. The barrel in the gun in question had the best results with 910-930 at longer ranges. The type of barrel seems to play a big factor in idea speeds for a given pellet. I just never expected this level of sensitivity with the 15gr JSBs, whereas the 18gr are more forgiving!
 
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I believe the gun can be more accurate with higher pressure than needed. You Are basically harmonic tuning the gun when testing out different pressure. Tuning at the knee is basically a "simple" way to reach a target velocity, and at the same time reach low ES . If you do not intend to shoot below regpressure you can test higher pressure also. So it probably can be, but does not have to:)


 
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Here is an example: My wildcat in .177 was setup with a regpressure of 105 bar with a huma reg. It had a max speed of about 930 fps. I started testing at about 910 fps shooting groups, and slowly turned out HS. Since I mostly shoot at 25m at my backyard, it was not that important to nesessary stay close to the highest setting. At that range, my goal is to get as close as possible to 1 hole group. It did shoot pretty well down to 880-870. when it reach 860-850 it seemed to open up a litle. when I got down to like 830-820 it seemed to be the most accurate so far. What I did discover was that the ES close to the maxspeed was very tiny. It then started to get wider as I turned out HS. But when I got even lower to like 840 (if I do not remember wrong) the ES seemed to thighten up again. And at 830-820 where the gun was most accurate, it did not quiet have the same low ES as on the higher setting, but the grouping was thighter. I do plan to shoot faster, and has now increased reg to 110 bar, and will slowly adjust HS in again, and see if I can get even better group at higher speed.

One might say the reason is that the gun just liked the lower speed (it could be the case). But I still believe it has to do something with the harmonics of the gun. I did earlier test with reg from 90 bar shooting at around 880 and lower, which also is closer to max speed, but that was still not as good as going low on 830 with higher pressure. My experiance so far is that my wildcat shoot better with a regpressure quiet a bit higher, than what is needed.
 
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@tor47 - yeah it could very well be harmonic effect.

I've also experienced oddities with accuracy at different ranges with the same settings, I was doing around 25 shot groups at 50 and pellets were landing left, but at 100 they would pull more right. I'm not sure that I can reproduce this problem though, I wound up changing reg pressure (lower) a couple of times after that, and it do not manifest itself again. 
 
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Maybe guns act different, but what I find interesting is that ES can go for small close to max speed, and then get wider as one turn hammer spring out. But then it can start to tighten up again as one turn it even further. I am just guessing it has to do with how the valve and hammer work together. Maybe somewhere inbetween the hammer does not open valve quiet as consistent when pressure is to "soft". When hammer spring then is turned further out, the pressure gets "harder" and the valve open and close more precisely? But going to far out it would probably start to widen up again, as now the hammer force is to weak?
 
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What is also interesting is the the gun does recoil even when dryfire without pellets. If you dryfire while looking true the scope the crosshair does jump a litle. It is better seen with high magnification. If you find a different combination between hammer and reg it jumps less. It can probably not be made as a measurment on how accurate the gun will be when shooting pellets, but it is interesting to know the gun itself can be the cause of less or more "recoil".
 
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@tor47 - yeah it could very well be harmonic effect.

I've also experienced oddities with accuracy at different ranges with the same settings, I was doing around 25 shot groups at 50 and pellets were landing left, but at 100 they would pull more right. I'm not sure that I can reproduce this problem though, I wound up changing reg pressure (lower) a couple of times after that, and it do not manifest itself again.
Click to expand...

Could you have had pellet spiralling going on? From the videos I've seen of spiralling this would explain why there is a left impact at some ranges and right impact at other ranges.
 
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