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- Thread starter Caliber 22
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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.
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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.
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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
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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.
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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.
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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
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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
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
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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.
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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
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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.
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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.
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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.
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.
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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.
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Last year a had a pellet shooting M3 500mm. I noticed the exact same thing with H&N 27gr hunting pellets. They did ok just under 900 fps but were phenomenal at 935-938fps. And that was out to 100 yards. So that’s where the gun stayed until I changed things up. Like Trucker said, it’s your barrel. Not external with harmonics but internally. Barrel harmonics with a pellet gun that has a solid barrel on it might be getting overemphasized lately.
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Yeah, it's pretty normal for some rifles and pellets to shoot best well below the max speed.
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"Normal is a relative term, often in the mind of the beholder, and especially as pertains airguns, airgunning and airgunners." - Abby Normal
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Well if you believe, then you have another rabbit hole to go down if you want to try to influence it. Will it be worth it? Only you can determine that.
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