Tuning a PCP

[Caliber 22]

My Artemis (Snowpeak) M22 is quite pellet picky. It shoots H&N Baracuda 18 the best when tuned at about 110 bar reg pressure and that is at 940fps, just below the max speed of 970fps.. One hole at 25 meter, 10 - 12mm at 50 meter and so on. Some other pellets are doing OK but not as good. JSB 18.13 never did good with this rifle. Well, I increased the pressure to about 160bar and changed to a stronger hammer spring. It does not have a plenum gauge so it is a guess according to shooting string to see when the speed change. I tuned it for JSB 25gr pellets and it is doing good, not as precise as the H&N but good enough. With the same reg pressure I tried JSB 18.13 and turned down the hammer after every few shots to se what happens. To my surprise it settled at 920fps and was doing very good at 25 meter, much-much better than it did previously. I did not check longer distances as the wind was strong and gusty and the longer ranges are not as protected as the 25 meter range which is sheltered between buildings and trees. The max speed with the JSB on this reg pressure is 1080fps, thus the 920fps is 160fps lower than the max. This is a bit confusing to me (I am still learning and will till the end) as the general rule is that a good tune is supposed to be somewhere on the knee, just below the max speed. With the reg set at 110 bar or other lower pressure the JSB 18 would never shoot good, no matter matter the speed and how much I adjusted pressure and hammer.

Question: Is this normal for some rifle / pellet combinations to shoot precise that much below the max speed, way below the knee?

 

[Joedirt199]

Gun may just not like JSBs. That is why people recommend shooting a wide range of pellet weights, diameters and brands to see what it likes.

 

[Caliber 22]

Gun may just not like JSBs. That is why people recommend shooting a wide range of pellet weights, diameters and brands to see what it likes.

Correct, that is what I know and that is why I tested many different pellets. But my question is, why is it shooting the JSB good at high pressure and that much below the knee which is not the general rule for tuning?

 

[Joedirt199]

So the JSB 18s don't shoot well at the same 920 fps velocity when tuned with a lower reg pressure but shoot better with a higher reg pressure at the same velocity. Difference between a hard fast blast of air and a slow steady blast of air.

 

[Stubbers]

So the JSB 18s don't shoot well at the same 920 fps velocity when tuned with a lower reg pressure but shoot better with a higher reg pressure at the same velocity. Difference between a hard fast blast of air and a slow steady blast of air.

Could be harmonics or the additional force against the pellet base however unlikely its the latter unless the difference in regulator settings is rather substantial.

In that case it is likely due to increased efficiency, because the 'hard fast blast of air' has more reduction of pressure as the projectile moves down the barrel resulting in less turbulence as the projectile exits the bore, the lower pressure setting requires the valve to be open longer, resulting in higher terminal pressure and thus more turbulence.

-Matt

 

[Gerry52]

Personally, I learned a long time ago to disregard "max fps speeds" as the bottom line in all this is where does my gun(s) shoot most accurately & efficiently. If I make a head shot at 895fps whatever I hit will be just as dead as if it was hit by a 1080fps projectile. Not one of my guns are set where the mfg says is the max fps. They're set at the most accurate fps for any particular gun.

 

[Vetmx]

Another thing to consider is this is not a one thing answer. Even though that’s what we all try to do to rationalize a problem or issue. It could be two or more things. Just a little of each that changes everything. But one thing is certain, a gun tuned 160fps under the plateau is more than likely not a great place to be from full fill to refill. But if it works for you and your needs with your pellet gun, do it. Your barrel, leade or both are your true problem. You just found a way to mask it with a certain pellet.

 

[Stubbers]

Another thing to consider is this is not a one thing answer. Even though that’s what we all try to do to rationalize a problem or issue. It could be two or more things. Just a little of each that changes everything. But one thing is certain, a gun tuned 160fps under the plateau is more than likely not a great place to be from full fill to refill. But if it works for you and your needs with your pellet gun, do it. Your barrel, leade or both are your true problem. You just found a way to mask it with a certain pellet.

For unregulated this couldn't be further from the truth, and for regulated, its ehhhhh, that tune will only present other flaws in the pcp be it regulator pressure output inconsistencies or hammer strike variability...

-Matt

 

[Stubbers]

A valve lift limiter for example has no issue reducing hammer strike variability due to reasons with the hammer/spring/its surface it rides on/angle of gun, but also inconsistent regulator output pressure as you'll be achieving near identical valve lift from shot to shot regardless of the force holding the poppet shut.

So tuning with a valve lift limiter in place (easy to integrate in any pcp) solves a lot of issues with tuning far below the plateau. However its a crutch and not needed if your regulator is functioning very well and your hammers travel is very minimal and more tolerant to changes in angle, temp, humidity, moon phase..ect.

-Matt

 

[Vetmx]

For unregulated this couldn't be further from the truth, and for regulated, its ehhhhh, that tune will only present other flaws in the pcp be it regulator pressure output inconsistencies or hammer strike variability...

-Matt

I think that gun is regulated. My response to just go for it stems from not everyone‘s PCP accuracy and distance needs have to match mine. Backyard Bill’s have been trilled with wonky guns with bad tunes for years. Horrible tunes can still drill pests at 50 yards. The gun is definitely pellet picky.

 

[Stubbers]

I think that gun is regulated. My response to just go for it stems from not everyone‘s PCP accuracy and distance needs have to match mine. Backyard Bill’s have been trilled with wonky guns with bad tunes for years. Horrible tunes can still drill pests at 50 yards. The gun is definitely pellet picky.

You stated a gun, not OP's gun...to be clear, not trying to nit pick but we were speaking in generalizations not specifics, but okay.


-Matt

 

[Vetmx]

You stated a gun, not OP's gun...to be clear, not trying to nit pick but we were speaking in generalizations not specifics, but okay.


-Matt

It’s his topic so I was talking to him about his gun. But I wouldn’t tune any gun 160fps below the plateau unless it was shooting 4,000fps. I stand behind my last two sentences as the real problem.

 

[357cal]

Personally, I learned a long time ago to disregard "max fps speeds" as the bottom line in all this is where does my gun(s) shoot most accurately & efficiently. If I make a head shot at 895fps whatever I hit will be just as dead as if it was hit by a 1080fps projectile. Not one of my guns are set where the mfg says is the max fps. They're set at the most accurate fps for any particular gun.

I've had a particular 357 for three years, and it was Robert Vogel who did all the work to discover that the optimal operating pressure was 3800 psi, not 4500 psi about 2 years ago, It was only a year ago that he revisited his findings and realized that the lower psi actually yielded faster fps. I have a 6.8-liter cf with an inline adjustable regulator. My experience was slightly different; it was a bit slower than his (as no two are identical), achieving around 340 fpe at 3300-3400 psi instead of 300 fpe at 3800 psi, which also conserved air. I noticed similar results with the Texan. The adjustable regulator greatly simplified the process. Thanks, Gerry52.

 

[Trucker3573]

I read your post as it shoots 18 gr H&N at tune (A )well…940 fps. At that tune (A )it does not shoot 18.1 well. That would be expected as it is too fast. Then you bumped settings up to to shoot 25 gr. They did fairly well as expected because these settings probably produced the correct speed for the heavier pellet. Then the jsb did good when you backed the hammer down to 920 fps which would be expected as you dropped into the correct speed for them. You slowed them down from tune (A). To me this has really nothing to do with running at or below the knee of the gun but pellet speeds. In my experience pellets have been pretty easy. You get them into their window of good velocity and they will perform even with a non perfect tune. Running at or just below the knee of the reg pressure is more about shot count and consistency. If you run there you will have better shot to shot consistency (velocity) and therefore better precision in your groups. The trick is to find the right regulator pressure that you can run just below the “knee” that gives the correct velocity. Your tune( A)
was just too hot for the jsb 18. Turn the reg down to a point your gun will run nice and consistent with those at 890 and I bet they will be money. They perform in most guns.

 

[Caliber 22]

Thanks for all the input.

Just to clear up some confusion, my quest is not maximum speed but maximum presision. The normal tune for this rifle is for H&N 18 grain at 940fps which is very precise when sorted by head size. As the tune for that is noted I can go back to that easily.

I want to test different pellets to know what my options for this rifle are. This setup was meant to test JSB 25 grain pellets, thus the higher pressure. Now I know the 25gr shoots well at this setup and noted everything to be able to go back to that when required. I still need to test it at longer distances up to 100 meter when the wind is calm and I have time for it.

Since I have a lot of JSB 18.13 pellets which does not shoot well with the normal lower pressure tune and I therefore not use it, I tested it with this higher pressure just out of curiosity. It happened to start at 1080fps, it was not my goal to shoot at that speed, it was just the starting point since the rifle setup was already there. It was not my intention to tune at 160fps below the plateau, I just happened to found that it works for this combination and will keep it at that when I want to use JSB 18.13, not for other pellets.

If I need more power I will use my .22LR or bigger CF rifles. The same with my .22LR, I use sub-sonic ammo and don't use HV ammo, again, if I need more power than that I use a bigger riffle.

The rest is explained above.

I think I found the answer in post # 4 & 5, thank you. The higher pressure allows for a shorter air spike which don't upset the pellet when leaving the muzzle. The longer, softer burst of air might upset the pellet by causing turbulence when the JSB 18.13 pellet leaves the muzzle and/or the barrel harmonics is different in each case.

 

[Caliber 22]

I read your post as it shoots 18 gr H&N at tune (A )well…940 fps. At that tune (A )it does not shoot 18.1 well. That would be expected as it is too fast. Then you bumped settings up to to shoot 25 gr. They did fairly well as expected because these settings probably produced the correct speed for the heavier pellet. Then the jsb did good when you backed the hammer down to 920 fps which would be expected as you dropped into the correct speed for them. You slowed them down from tune (A). To me this has really nothing to do with running at or below the knee of the gun but pellet speeds. In my experience pellets have been pretty easy. You get them into their window of good velocity and they will perform even with a non perfect tune. Running at or just below the knee of the reg pressure is more about shot count and consistency. If you run there you will have better shot to shot consistency (velocity) and therefore better precision in your groups. The trick is to find the right regulator pressure that you can run just below the “knee” that gives the correct velocity. Your tune( A)
was just too hot for the jsb 18. Turn the reg down to a point your gun will run nice and consistent with those at 890 and I bet they will be money. They perform in most guns.

I already typed post #15 when you posted this.

Previously I did try proper tunes at lower pressures from 110 bar down to about 80 bar and from 940fps down to 700fps with the JSB 18.13 and it just did not work.

 

[Caliber 22]

Turn the reg down to a point your gun will run nice and consistent with those at 890 and I bet they will be money. They perform in most guns.

Even the H&N 18 does not shoot as presice at 890fps as 940fps out of this rifle, no matter the pressure or tune. I did try a lot

 

[Trucker3573]

I already typed post #15 when you posted this.

Previously I did try proper tunes at lower pressures from 110 bar down to about 80 bar and from 940fps down to 700fps with the JSB 18.13 and it just did not work.

Very weird as they work in just about anything I’ve ever shot at mid 8’s to just over 900.

 

[Trucker3573]

Even the H&N 18 does not shoot as presice at 890fps as 940fps out of this rifle, no matter the pressure or tune. I did try a lot

Funky barrel I would say.

 

[ThisIsWhyIWant]

Yeah, it can happen. Some rifles just like certain pellets at lower speeds, even if it goes against the usual tuning advice. My own air rifle prefers certain pellets at speeds I wouldn’t have expected to work well. If it’s grouping well at 920fps, I’d stick with it.