Pellet Spiraling and Barrel Twist Rates..

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NAIRBOG

Member
Feb 6, 2020
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Davao del Sur, Philippines
i would like to learn more about pellet spiraling, i kept looking and scrolling for discussions about spiraling of the pellets (22 cal.) it seems like people are not that concerned about it, ill bet almost all owners of pcp's who wants to shoot at longer distances like 100-150 yards cannot have a good group and the main reason for that is pellet spiraling without them even knowing.. .. i believe that having barrel with a fast twist rate like 1:14 or 1:6 or even 1:17 shot at >850 fps will give you spiraling at a hundred yards... if im wrong about this, can anyone show a video proving that a pellet can be stable with a high twist rate? thankyou.. =)
 
As an experiment and was warned it won't be successful ... Damn !! Had access to a TJ's .30 cal in 1-11 twist that was able to be test fitted into a gun I had that could make the power in .30 cal. ( WAR Warp )

Shooting the JSB 44 grain at @ 870 fps the pellets not only spiraled severely, but did so right out of the muzzle and continued as distance. WHAT A SCATTER GUN !!!

OVER STABILIZED by excessive RPM on a short pellet is very real !! When asking a fellow Forum member what .30 could be shot in a 1-11 came back with 150-165 grains LONG slug at over 900 fps. Well thats not going to happen with an Air Gun !! Barrels a paper weight now.
 
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thankyou sir nervousrig... new learnings from that thread... lots of friends here claiming no spiraling at 120 yards with their LW barrels with 1:17 twist at 900 fps.. i dont know how that is possible.. anyone here can prove groupings at 100 yards with high twist barrels?
Click to expand...

I think that we can further define that there is a point with pellets and twist rate where the spin rate to pellet speed ratio gets to a point that the pellet becomes unstable. With very slow twist rate barrels like the older FX ST barrels that have an effective twist rate between 1:30 and 1:50 (depending where you look) the ratio never increases to a point where the pellet becomes unstable. I've watched the 44.75 grain pellet out of my .30 FX Bobcat out past 200 yards and it was still flying in a stable arc. This also seems to be true for newer design pellet barrels with low twist rates...

What I think happens is that for a given pellet, pellet speed, and twist rate (spin) there is a point where the ratio increases to a point where the pellet becomes unstable.. So as the pellet exits the barrel, the spin to speed ratio is the lowest. As the pellet travels downrange, the speed of the pellet decreases more proportionally than the spin, so the spin/speed ratio increases, and at a point the pellet becomes unstable.

I've watched this happen in my .22 EDgun R3 Long with RD Monsters. (1:16 twist). I had the speed set to 925 FPS, and at 100 yards it was stable and accurate, capable of MOA groups. But just ten yards further, at 110 yards, the pellet had lost stability and couldn't group inside a softball sized group. Now here's the point that confuses me. I increased the speed to 960 FPS. Still good at 100 yards (even better than 925), but at 110, 115, and 125 yards the pellet was still stable. I can only guess that the additional speed moved the instability curve based on spin/speed further to the right. I haven't tried it past 125 yards, but it'll shoot MOA at 115 yards...

And that's my wingnut theory... ;)
 
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thankyou sir nervousrig... new learnings from that thread... lots of friends here claiming no spiraling at 120 yards with their LW barrels with 1:17 twist at 900 fps.. i dont know how that is possible.. anyone here can prove groupings at 100 yards with high twist barrels?
Click to expand...

I think that we can further define that there is a point with pellets and twist rate where the spin rate to pellet speed ratio gets to a point that the pellet becomes unstable. With very slow twist rate barrels like the older FX ST barrels that have an effective twist rate between 1:30 and 1:50 (depending where you look) the ratio never increases to a point where the pellet becomes unstable. I've watched the 44.75 grain pellet out of my .30 FX Bobcat out past 200 yards and it was still flying in a stable arc. This also seems to be true for newer design pellet barrels with low twist rates...

What I think happens is that for a given pellet, pellet speed, and twist rate (spin) there is a point where the ratio increases to a point where the pellet becomes unstable.. So as the pellet exits the barrel, the spin to speed ratio is the lowest. As the pellet travels downrange, the speed of the pellet decreases more proportionally than the spin, so the spin/speed ratio increases, and at a point the pellet becomes unstable.

I've watched this happen in my .22 EDgun R3 Long with RD Monsters. (1:16 twist). I had the speed set to 925 FPS, and at 100 yards it was stable and accurate, capable of MOA groups. But just ten yards further, at 110 yards, the pellet had lost stability and couldn't group inside a softball sized group. Now here's the point that confuses me. I increased the speed to 960 FPS. Still good at 100 yards (even better than 925), but at 110, 115, and 125 yards the pellet was still stable. I can only guess that the additional speed moved the instability curve based on spin/speed further to the right. I haven't tried it past 125 yards, but it'll shoot MOA at 115 yards...

And that's my wingnut theory... ;)
Click to expand...

"here's the point that confuses me. I increased the speed to 960 FPS. Still good at 100 yards (even better than 925), but at 110, 115, and 125 yards the pellet was still stable. "

Very interesting, especially in light of all the advice about 850 to 900 being the "ideal" for pellet stability and the need to "slow them down". Seems there is often no general "ideal", just a best specific. I have noted excellent stability from my .177 Condor with Beasts and Monsters at around 1000 fps but I don't regularly shoot beyond about 70 to 80 yards maximum, just no interest in it for me. Good to see stability at even 125 yards in this instance.

 
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Keep in mind that every pellet has a different shape and will have a different reaction to the variables.. For example, people who are shooting the Hades pellet are commenting that they are having good results at speeds higher than other pellets will tolerate . My theory is that the cut outs, where the Hades are meant to expand, allow the shockwave from the pellet head to pass by the diabolo waist of the pellet. 

Theory is good, but empirical data is King. 
 
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Keep in mind that every pellet has a different shape and will have a different reaction to the variables.. For example, people who are shooting the Hades pellet are commenting that they are having good results at speeds higher than other pellets will tolerate . My theory is that the cut outs, where the Hades are meant to expand, allow the shockwave from the pellet head to pass by the diabolo waist of the pellet. 

Theory is good, but empirical data is King.
Click to expand...

Interesting thought, but it seems that even with a simple dome shape that the shock wave would be away from the waist. Could be something to the idea though.
 
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Keep in mind that every pellet has a different shape and will have a different reaction to the variables.. For example, people who are shooting the Hades pellet are commenting that they are having good results at speeds higher than other pellets will tolerate . My theory is that the cut outs, where the Hades are meant to expand, allow the shockwave from the pellet head to pass by the diabolo waist of the pellet. 

Theory is good, but empirical data is King.
Click to expand...

This guy knows his stuff.
 
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I've watched this happen in my .22 EDgun R3 Long with RD Monsters. (1:16 twist). I had the speed set to 925 FPS, and at 100 yards it was stable and accurate, capable of MOA groups. But just ten yards further, at 110 yards, the pellet had lost stability and couldn't group inside a softball sized group. Now here's the point that confuses me. I increased the speed to 960 FPS. Still good at 100 yards (even better than 925), but at 110, 115, and 125 yards the pellet was still stable. I can only guess that the additional speed moved the instability curve based on spin/speed further to the right. I haven't tried it past 125 yards, but it'll shoot MOA at 115 yards…



this is very interesting... this is exactly what my friends advised me to do, they even wanted me to try 1020 fps shooting 150 yards with jsb 18.13 gr. in a 1:17 twist barrel, because that was their current set-up.. which is very hard to believe with all the information/videos im getting from the experts... and 1030 is in transonic zone right? maybe ill try and film it after this covid problems we have.. ill try to post videos soon...
 
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It is the ratio of the two drags and stabilization effects is why the pellets going faster can avoid the spiral longer but eventually they will also be overcome by this....just further down range. Pellets lose speed faster than their spin rate slows down. By increasing the speed you can increase the distance before this transition happens. The better the pellet BC, the longer down range before they lose enough speed as well.

There are other factors related to the aerodynamics and drag in play as well. A pellet with less drag stabilization will have less propensity spiral.

Here is where I start guessing. Is it possible a pellet with a textured tip, like the Hades or H&N Hunter Extreme would have more spin drag? If so, this would help extend the point where the ratio between spin stabilization vs. drag stabilization became an issue.
 
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this is very interesting... this is exactly what my friends advised me to do, they even wanted me to try 1020 fps shooting 150 yards with jsb 18.13 gr. in a 1:17 twist barrel, because that was their current set-up.. which is very hard to believe with all the information/videos im getting from the experts... and 1030 is in transonic zone right? maybe ill try and film it after this covid problems we have.. ill try to post videos soon...
Click to expand...

Should be sub-sonic, and I think you would have to keep it there.I believe the sound barrier is 1,100 fps, plus or minus, depending on conditions. 
 
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It is the ratio of the two drags and stabilization effects is why the pellets going faster can avoid the spiral longer but eventually they will also be overcome by this....just further down range. Pellets lose speed faster than their spin rate slows down. By increasing the speed you can increase the distance before this transition happens. The better the pellet BC, the longer down range before they lose enough speed as well.

There are other factors related to the aerodynamics and drag in play as well. A pellet with less drag stabilization will have less propensity spiral.

Here is where I start guessing. Is it possible a pellet with a textured tip, like the Hades or H&N Hunter Extreme would have more spin drag? If so, this would help extend the point where the ratio between spin stabilization vs. drag stabilization became an issue.
Click to expand...

Excellent line of thought. So many variables and so difficult to accurately quantify/analyze but this idea sure seems logical. A + for you. Would probably require ultra high speed photography to verify.
 
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Hi All,

I wanted to thank you all for one of the (IMHO) better reads in a while!

I have been fortunate to play with some FX, AGT, Edgun and Kalibrgun products, all under ideal conditions, I wanted to add what I observed.

I agree with just about all the noted observations above regarding projectile profile, speed, twist rate and downrange stability at long range(100y+). For a while I have been pushing pellets down my barrels while polishing, to look for spots in the barrel to focus on. I eventually started to pay attention to the shape of the pellet after being pushed, what I noted was that the rifles that produced a round pellet seemed to provide better stability at 100+ with regards to spiralling.

A few months back there was a subtle change to the choke procedure on STX barrels, the good ones that I have played with have been producing more circular vs pentangular pellets and the result downrange for me has been good to great!

The .22 STX slug liners that I got to play with have had a particularly round crown, and seem to love 18.1 JSBs at approx 950FPS, this is totally contrary to the accepted 880 fps for .22 JSB!

The point is that my experience seems to back the above theories of:

Good projectile=good drag (in the barrel and through the air as it flies) but, good needs to be looked at after the thing has left the barrel not only before you load it...

Speed and spin do funky things=one needs to manage for this by sacrificing range or speed or accuracy. If you have a barrel that shoots well at the range you like then put it in the safe!

I need to add that changing a liner or 9 is much easier than changing a whole gun that just doesn't shoot.


 
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It seems there are factors in the barrel lottery that we might not understand or at least know how much our individual barrels are effected by those variables. It is easier to evaluate a good crown and barrel finish than it is to observe the roundness of a projectile after being pressed through the barrel.

I agree. If you get a good one don't let it go!


 
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Nairbog, that’s an interesting rationale that Daniel presents, that the increased velocity may potentially extend the distance at which spiraling begins. On its surface, it sounds plausible so I’m interested to see if it works out that way in some cases. All the accounts I’ve seen have said the opposite however, that dropping the velocity was necessary to reduce or eliminate spiraling. In the scenario being discussed here, let’s just say the original velocity was 900fps and we’re considering cranking it up to the 1020fps figure that was mentioned, the increase in drag is going to cause a substantial portion of this added velocity to be lost fairly quickly. It will have a spin rate almost 20% faster (46,000rpm vs 38,000rpm), so while the velocity is being lost at an even faster rate, the RPMs are considerably higher. (As a side note, wind drift will also be worse at this high muzzle velocity).

FWIW, I’ve since learned from Miles, a former ballistics engineer, that my reasoning (same as Daniel’s) in the earlier thread is flawed…referring to high drag, imagined as a parachute trailing behind the pellet, serves as a counteracting force to the tendency for the pellet to develop a spiral as it loses velocity (while maintaining a significant portion of its spin rate). From a practical perspective, it does seem to serve our layman’s purposes well enough, much as the distinction that pellets are flare stabilized, not drag stabilized, doesn’t substantially alter my picture of why a pellet needs less “help” than a cylindrical projectile to be stable. Nonetheless, it’s incorrect so I will refrain from repeating it in the future. Correct outputs from wrong inputs and all that :)

If you’re interested, Miles has published a very nice summary of forces affecting stability of pellets in this thread:
https://www.gatewaytoairguns.org/GTA/index.php?topic=169459

 
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