Is there a maximum effective distance for pellets.. Yes! And it can be predicted

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broekzwans

broekzwans

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Mar 13, 2016
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the Netherlands
So, let’s first set some expectations straight: this topic is not about predicting the group size at distance, nor about terminal performance etc. It is about predicting the distance where the danger zone of (self-)destabilization of pellets will start. For those who follow me on instagram might have already seen this topic pass their feed a couple times in the past year:

First post: https://www.instagram.com/p/COa_To4BvlG/ (keep in mind that not all of it is perfectly explained, it’s a topic that is still being studied and I had to start somewhere ;) ).

Matt Dubber, Ted Bier and some others have done a great job in identifying factors which have an influence on stability of pellets.

pic_1.1638993840.jpg




Despite that I was still missing an explanation of what and when it happens down range. @bushwacker and I were both thinking about this and by combining experiences of testing a lot of different pellets (and slugs) with some theories we came up with something. The goal was to be able to predict the maximum effective distance of a pellet before it gets into the danger zone of instability.

After monitoring a lot of spiralling of different pellets at long distances we started looking for variables to predict the instability. Let’s start breaking down of what is investigated to find a relation:

  • One of the first that comes up is downrange velocity. This wasn’t consistent enough to solely use for predicting it since there is a difference with varying twist rates and muzzle velocities. Read: there was not just a fixed downrange velocity at where it starts to spiral.
  • twist rate: same idea as mentioned at downrange velocity.
  • Pellet itself: length, weight, etc. No straightforward conversion factor or whatever to find a relation between the destabilization distance/velocity and the sizes of the pellet.
  • Gyroscopic stability factor: this one is a bit tricky because it in most cases only tells you something about what happens at the muzzle. Add to that that the standard stability formulas are not made for pellet shapes.
  • Ballistic coefficient: also, no straightforward conversion factor or ratio could be translated to the observations.
  • Spin rate: this is the relation between muzzle velocity and twist rate and gives the rpm value of your projectile. Also, no direct relations here.

Let’s dive a bit more into what we see:

pic_2.1638993858.jpg




The picture above is important for understanding what is happening. During stable flight the centre of pressure (CP) is behind the centre of gravity (CG) for flare stabilized projectiles (yes you read it correctly; pellets are flare stabilized, not drag stabilized 😉 ). What is important here is that the centre of pressure (CP) stays behind the centre of gravity (CG) with a certain margin. Think of it like this: the centre of pressure (CP) varies during the flight; it moves inwards towards the front of the pellet while it’s slowing down, and at a certain point the CP and CG (centre of gravity) reach a position where the ratio between the pellet’s rotational inertia (combination of spin rate and weight distribution along the radius), forward momentum and CP-CG margin becomes critical. Combine that with the weight distribution of a pellet, which is the skirt weight attached to the head weight via the small waist -> roughly said a dumbbell weight distribution. Taking all of this into account to try to answer the following question: do pellets have a (self-inflicting) destabilization at some point which is either easily triggered by an outside force or can start by itself. And most important: how to predict this point or range?

By looking at pictures and easily available numbers the problem couldn’t be solved. So, what do you start doing as a curious engineer which refuses to believe this behaviour is random or unpredictable: start crunching numbers until a relation can be found 😊.

I’ve made a sheet to start the crunching:

pic_3.1638993877.jpg




I started out with a mix of pellets and slugs to see if a relation could be established but that ended quite quickly. From gut feeling we knew it must have something to do with the downrange stabilisation, but it took me some time to find a relation there.

By using some reverse engineering from the observed data while pellet testing and linking it to the downrange equivalent stability factor progress started to appear. In this sheet you can see that the stability factor increases over distance (read it ‘stabilises’ more in the case of slugs and bullets) but it will show that this is actually a very important number (not specifically in a way you would expect).

After a lot of number crunching, re-adjusting theories and expectations, the result started showing that there seems to be a relation between the dimensions of the pellet and a certain downrange equivalent stability factor. Around a certain value of this downrange stability factor (and thus a downrange velocity) pellets start to spiral or just need a slight or sudden push from the wind to start spiralling. Since I couldn’t find an exact number at which this starts to happen, because it’s not a case of slowing down that 1 m/s (or fps) and suddenly it’s out of control, I would prefer to call it entering the danger zone. The danger zone is the dowrange velocity zone where there is a high risk of self-destabilisation or with the slightest stimulus it goes out of control.

Some assumptions that had to be made to keep it sort of simple:

  • To calculate the stability factor I used the Miller theorem, I know this is not made for pellets but at least it works as a solid base in these calculations.
  • Spin rate is an important factor to calculate downrange twist rate equivalent for using it in the Miller theorem. During flight the spin rate decreases but this was very difficult to predict. I’ve asked Applied Ballistics (Bryan Litz his company), they said they were going to look into it but no response yet.

Now, where can we use this info for: I’ve put all my formulas in Matlab (nerd program for mathematics) to solve the formulas for me.

pic_4.1638993906.jpg




This curve shows what the downrange destabilization velocity estimation is vs the twist rate of the barrel for the 18.1 grain JSB Heavy in .22 at 275 m/s at 20 degrees Celsius. As soon as the downrange velocity of the pellet goes into the red area of the graph it is in the danger zone for destabilization. When I run these numbers through a ballistics calculator it can be translated to actual distances:

pic_5.1638993921.jpg




A conclusion that can be drawn from these graphs is that slow twists help in long range performance for pellets by delaying the self-destabilization.

Funny thing: slugs/bullets need a minimum stability Sg value of 1.5 to expect maximum BC to be reached and to be gyroscopically stable, with pellets the exact opposite behaviour is seen. Pellets seem to have a maximum downrange equivalent stability number at which they are expected to remain stable.

I can run these numbers for basically any pellet. To verify the theory, we’ve compared the numbers to observations, and it seems to match quite accurately but some finetuning is still required. I’m also working on writing a program which allows this theory to be used by basically anyone, but this will take some time.

Disclaimer, this is still just a theory which I wanted to share but I’m looking for more data to verify the validity. So predictions can be made but don’t shoot the messenger if your experience deviates slightly from the numbers. Feel free to think along, input is welcome :)
 
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predicted in relation to what, speed or range? .. i think one of the main factor sets in play with a pellet at long range is a pellets shape is designed to make it fly via skirt drag etc ... now factor in a barrel at an elevated angle shooting long range and the pellets pronounced flight arc ... the pellet leaves at a positive angle related to the ground and 'twist' inserts a gyroscopic affect that works with it up until the 'down' side of the arc .. now gyroscopic forces tend to hold the pellet at a positve 'up pointed' angle and drag is starting to hit it from the bottom as it falls on the far downward side of the arc .. these opposing forces are most likely where instability sets in and it likely 'starts' somewhere near the top of the path arc .. you have likely seen the results of this on paper before with a most common 'nose up' side imprint of a pellet ... of coirse if its far enough and the nose wint up way back its tumbled to any random position ..
 
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What happens when you apply your theory to a pellet shot with no spin? Not being a smart ass here, I didn't really grasp your theory on first reading and will go over it in more detail when I have more time.

Interesting project.
Click to expand...

that was out of scope 😅 Actually hard to predict what will happen, in general no spin is not really used for long range accuracy :p

If you have questions just ask. It's sometimes hard to describe something in easy terms when you've been working on it for a long time
 
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broekzwans,

Wow! You have obviously put in a LOT of time and effort and contemplation(+ Green accuracy ball for effort and contribution). A lot of good info and an interesting idea to try to establish a correlation for pellet destabilization "danger zone" distance using other measurable data. 

It may be difficult to find a spin rate correlation that works for all shapes of pellets, though. I think @dizzums hit on something mentioning the SHAPE of the pellet in his post(although it was hard to follow because of the run-on sentences/lack of punctuation). Pellets behave differently than slugs, as you have stated, with respect to stabilization(flare drag vs gyro). I have found that small-waisted, badminton shuttlecock shaped pellets(like the JSB Jumbo Heavy 18.13g that you mentioned) perform noticeably different(particularly at longer ranges) than non small-waisted pellets(like JSB Monster Redesigns) with respect to what muzzle velocities and/or twist rates are used. The JSB MRDs generally need high MV and a little higher twist rate to perform better at longer ranges(more like what you would use when shooting a slug). Drop the MV and/or twist rate enough and increased pellet spiralling can be witnessed through the scope, as well as, group size opening up(and/or more wild "flyers") at the aforementioned longer ranges. The effect is even more noticable(or at least at closer distances) when shooting .177 JSB 8.44g vs JSB 10.34g Heavies or 13.43g Monsters. These are just some things I have noticed from my own shooting experiences and have read others post about.

Perhaps you can establish a destabilization distance correlation which would work with ALL shapes of pellets, or at least one which would be unique to the shape of projectile?

Thanks for the interesting post and good luck on your future research and testing!

Regards,

Phil
 
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broekzwans,

Wow! You have obviously put in a LOT of time and effort and contemplation(+ Green accuracy ball for effort and contribution). A lot of good info and an interesting idea to try to establish a correlation for pellet destabilization "danger zone" distance using other measurable data. 

It may be difficult to find a spin rate correlation that works for all shapes of pellets, though. I think @dizzums hit on something mentioning the SHAPE of the pellet in his post(although it was hard to follow because of the run-on sentences/lack of punctuation). Pellets behave differently than slugs, as you have stated, with respect to stabilization(flare drag vs gyro). I have found that small-waisted, badminton shuttlecock shaped pellets(like the JSB Jumbo Heavy 18.13g that you mentioned) perform noticeably different(particularly at longer ranges) than non small-waisted pellets(like JSB Monster Redesigns) with respect to what muzzle velocities and/or twist rates are used. The JSB MRDs generally need high MV and a little higher twist rate to perform better at longer ranges(more like what you would use when shooting a slug). Drop the MV and/or twist rate enough and increased pellet spiralling can be witnessed through the scope, as well as, group size opening up(and/or more wild "flyers") at the aforementioned longer ranges. The effect is even more noticable(or at least at closer distances) when shooting .177 JSB 8.44g vs JSB 10.34g Heavies or 13.43g Monsters. These are just some things I have noticed from my own shooting experiences and have read others post about.

Perhaps you can establish a destabilization distance correlation which would work with ALL shapes of pellets, or at least one which would be unique to the shape of projectile?

Thanks for the interesting post and good luck on your future research and testing!

Regards,

Phil
Click to expand...

Hi Phil,

Thanks for your response! The graph I included is not a one size fits all, it is very specific to the 18.1 grain pellet at 275 m/s. For every other pellet (pellet dimensions is important here) and muzzle velocity you get a different graph (and tuning parameter), maybe I should have included some more to make this clear 😅 What I'm trying to implement is a tuning parameter that is linked to a certain pellet's design so it becomes a bit more precise than a general tuning parameter. The graphs I used now are based on twist rate but I can also base them on a fixed twist and change the muzzle velocity, or map them in 3D with both twist rate and muzzle velocity included. Lot's of things to explore but I wanted to show that some research is running and input is welcome 😁

The MRD is a bit of an oddball among pellets which I could not fully predict yet. Normally when you push it harder you will run into more problems but the MRDs need the speed to perform somewhat stable, although it has some quirks when it comes to bursts of wind or sudden change of environmental conditions.
 
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That's a hard problem to solve for. I've never imagined that there was any tight linearity to pellet destabilization due to variables with dynamic effects and variability with the shape of the pellets (and defects). Gravity is pretty constant lol, but in my mind everything else will affect the ballistic coefficient decomposition differently in an non-simulated "real world" scenario.

It would be interesting if there was a lot of solid (and diverse) data to see what the high and low watermarks would be in different environmental conditions for a given pellet, with different barrel twist rates and such. Might be able to build scientifically a CDP for different pellets, and determine the ideal barrels twist rates. 

My best guess though would be that stability would be maximized the longer CG remains closer to center. 
 
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broekzwans,

Ah, ok. I understand what you are doing a little better now. In my shooting experience, the 18.13g destabilization is not the major limiting factor of choosing that pellet for (BR competition or hunting)accuracy as they group well for me out to 100 yards in CALM conditions, with few to no wild "flyers". Lack of resistence to WIND effects is the major limiting factor for not choosing that pellet to shoot. MRDs are a much better PELLET choice for 50 or 100 yard competition BR shooting because of their higher BC/greater resistance to being pushed around by the wind. In "real world" (outdoor)competition/hunting conditions, there is going to be wind. And by far, it is the hardest variable to deal with. However, (because of their shape and/or inconsistencies in manufacturing?), the MRDs are much more prone to destabilization(if shot at too low/high speed and/or too low/high of a twist rate) and produce (comparatively) more wild "flyers" which will ruin an otherwise good competition BR target/score. 

Same problem with (mainly .177 caliber)Field Target(sub 12 ft/lbs) competition which mainly use 8.44g(small waisted, badminton shuttlecock shaped) vs 10.34g(non-small waisted, non-badminton shuttlecock shaped). And Hunter Field Target(sub 20 ft/lbs) competition which use 8.44g, but tends to be dominated by 10.34g or 13.43g. Both of the latter are non-small waisted(i.e.-harder to stabilize compared to small-waisted pellets, but have tremendous BC advantage and are generally less affected by wind). Fortunately, at sub 20 ft/lbs, they can be shot fast enough and impart a fast enough spin to keep them stabilized(limit spiraling and wild flyers) out to the max distance of 55 yards. With the lower sub12 ft/lb power limit on FT guns, it becomes harder to stabilize the 10.34g enough out to 55 yards.

I get that you are probably carefully and methodically trialing/testing/checking, "crunching numbers", and accruing useful data/correlations and building on that. I salute you for it. And no one can solve the biggest problems "overnight", so the 18.1g(very popular pellet) is as good a pellet as any to start with. But if you ever make any inroads into predictive analytics regarding the performance of the aforementioned JSB MRDs, 10.34g, or 13.43g pellets, many 50 and 100 yard Benchrest, FT, and HFT shooters, as well as, many hunters and plinkers, and myself will be VERY interested in your results!

Good luck and keep up the good work!
 
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I l8ke what you're doing ! On GTA there are a couple of very informative threads of similar research. It's extremely interesting.

My own experiences are that at 17.7 twist, the 177, 10.3s and 8.4 pellets are stable past 150 but of course, not very useable because of wind. The 22 cal 25.4s have stayed stable out to 289 in 1 in 17.7"... the farthest I've shot them. The 18.1s have been good to 200, though wind is a big issue. The 25 cal 33.4s fall apart after 220 so are very bad by 289.... 1 in 30" twist. The 30 cals seem to be stable at 289, but blow in the wind so much more than the 25 and 22 cal, I don't shoot them much.... 1 in 30" twist.

The one I'm VERY interested in is the 177 16.1s. They seem PHENOMENAL at 50 and really good at 75 but by 100, there are many fliers... 1 in 17" twist. I would really like to try different twist rates but LW has only 17.7, 20 and 30 twist rates but the slow ones are only available in 16 mm. I would have turn them down to 15mm and that affects the bore diameter a little. So... In order to keep it simpler, it would really be good to know if it needs faster or slower twist than 17.7

Anyway, I'm following your research with great interest. Thanks much for sharing.

Bob
 
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That's a hard problem to solve for. I've never imagined that there was any tight linearity to pellet destabilization due to variables with dynamic effects and variability with the shape of the pellets (and defects). Gravity is pretty constant lol, but in my mind everything else will affect the ballistic coefficient decomposition differently in an non-simulated "real world" scenario.

It would be interesting if there was a lot of solid (and diverse) data to see what the high and low watermarks would be in different environmental conditions for a given pellet, with different barrel twist rates and such. Might be able to build scientifically a CDP for different pellets, and determine the ideal barrels twist rates. 

My best guess though would be that stability would be maximized the longer CG remains closer to center.
Click to expand...

The dynamic effects of wind, clipping etc are not taken into account here, this is about the destabilization that happens even in indoor conditions with practically no extra influences. With a couple of people we combined what we saw and measured (just like what bob mentioned) and based on that we started crunching numbers to see if we could find relations.

What we basically saw was that twist rate and muzzle velocity had the biggest influence on influencing the downrange stability of a pellet. There is of course a difference between the different shapes of pellets so these graphs are custom to each pellet, muzzle velocity, twist rate, BC (which has a barrel dependency 😅).

CG is basically determined by design and won't change as long as the pellet remains in the same shape and weight. CP will change depending on angle of attack, velocity and some more influences. There is a static margin described for flare/fin stabilized projectiles for the relative position of CG and CP:

static margin B = ( (x_CP - x_CG)/length ) x 100%

For fin stabilized projectiles a steady state static margin of greater than 10% will keep it stable, couldn't really find what margin to use for flare stabilized projectiles but once CP goes in front of CG it will start tumbling. The relation in this is at least that the relative positions of CP and CG are critical to it's stability. (there are some very interesting papers on the internet about this but most are aimed at supersonic rockets/projectiles).

Based on this I also have a feeling that this has a lot to do with the stability of projectiles like the monster redesigneds, their CG is pretty far back so you need speed to push CP behind it with sufficient margin to keep it stable at distance.

I'm planning to make a request for more data on pellets so this is not only built on our local experiences and can be compared to others results. Would be nice to see if my estimations hold up with different conditions, height etc.
 
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broekzwans,

Ah, ok. I understand what you are doing a little better now. In my shooting experience, the 18.13g destabilization is not the major limiting factor of choosing that pellet for (BR competition or hunting)accuracy as they group well for me out to 100 yards in CALM conditions, with few to no wild "flyers". Lack of resistence to WIND effects is the major limiting factor for not choosing that pellet to shoot. MRDs are a much better PELLET choice for 50 or 100 yard competition BR shooting because of their higher BC/greater resistance to being pushed around by the wind. In "real world" (outdoor)competition/hunting conditions, there is going to be wind. And by far, it is the hardest variable to deal with. However, (because of their shape and/or inconsistencies in manufacturing?), the MRDs are much more prone to destabilization(if shot at too low/high speed and/or too low/high of a twist rate) and produce (comparatively) more wild "flyers" which will ruin an otherwise good competition BR target/score.
Click to expand...

I just used the 18 grains as an example because I had the data available, could have chosen any other pellet for the explanation.

The predictability of the 18 grains makes them much more useful for me than the unpredictable MRDs in changing conditions 😜 



broekzwans,

Same problem with (mainly .177 caliber)Field Target(sub 12 ft/lbs) competition which mainly use 8.44g(small waisted, badminton shuttlecock shaped) vs 10.34g(non-small waisted, non-badminton shuttlecock shaped). And Hunter Field Target(sub 20 ft/lbs) competition which use 8.44g, but tends to be dominated by 10.34g or 13.43g. Both of the latter are non-small waisted(i.e.-harder to stabilize compared to small-waisted pellets, but have tremendous BC advantage and are generally less affected by wind). Fortunately, at sub 20 ft/lbs, they can be shot fast enough and impart a fast enough spin to keep them stabilized(limit spiraling and wild flyers) out to the max distance of 55 yards. With the lower sub12 ft/lb power limit on FT guns, it becomes harder to stabilize the 10.34g enough out to 55 yards.

I get that you are probably carefully and methodically trialing/testing/checking, "crunching numbers", and accruing useful data/correlations and building on that. I salute you for it. And no one can solve the biggest problems "overnight", so the 18.1g(very popular pellet) is as good a pellet as any to start with. But if you ever make any inroads into predictive analytics regarding the performance of the aforementioned JSB MRDs, 10.34g, or 13.43g pellets, many 50 and 100 yard Benchrest, FT, and HFT shooters, as well as, many hunters and plinkers, and myself will be VERY interested in your results!

Good luck and keep up the good work!
Click to expand...

I can run the numbers soon, shall I use the energy numbers you stated and turn them into muzzle velocities? Do I need to know specific BCs you're using to calculate the downrange velocity into a distance?

I'm running everything in metric units by the way, meters is easy for me to turn into yards in the graphs so I can have a look at that but all the others I will just use metrics 🙃
 
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I l8ke what you're doing ! On GTA there are a couple of very informative threads of similar research. It's extremely interesting.

My own experiences are that at 17.7 twist, the 177, 10.3s and 8.4 pellets are stable past 150 but of course, not very useable because of wind. The 22 cal 25.4s have stayed stable out to 289 in 1 in 17.7"... the farthest I've shot them. The 18.1s have been good to 200, though wind is a big issue. The 25 cal 33.4s fall apart after 220 so are very bad by 289.... 1 in 30" twist. The 30 cals seem to be stable at 289, but blow in the wind so much more than the 25 and 22 cal, I don't shoot them much.... 1 in 30" twist.

The one I'm VERY interested in is the 177 16.1s. They seem PHENOMENAL at 50 and really good at 75 but by 100, there are many fliers... 1 in 17" twist. I would really like to try different twist rates but LW has only 17.7, 20 and 30 twist rates but the slow ones are only available in 16 mm. I would have turn them down to 15mm and that affects the bore diameter a little. So... In order to keep it simpler, it would really be good to know if it needs faster or slower twist than 17.7

Anyway, I'm following your research with great interest. Thanks much for sharing.

Bob
Click to expand...

Hi Bob, I will check GTA for the topics, would be interesting 👍

I will run some calculations for the projectiles you are mentioning. Can you maybe tell a bit more about the specific muzzle velocities, BC and environmental conditions you're shooting? Doesn't have to be exact but it creates some differences if I calculate them at sea level vs 3km above sea level 😊
 
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The dynamic effects of wind, clipping etc are not taken into account here, this is about the destabilization that happens even in indoor conditions with practically no extra influences. With a couple of people we combined what we saw and measured (just like what bob mentioned) and based on that we started crunching numbers to see if we could find relations.
Click to expand...

What we basically saw was that twist rate and muzzle velocity had the biggest influence on influencing the downrange stability of a pellet. There is of course a difference between the different shapes of pellets so these graphs are custom to each pellet, muzzle velocity, twist rate, BC (which has a barrel dependency
1f605.svg
).

CG is basically determined by design and won't change as long as the pellet remains in the same shape and weight. CP will change depending on angle of attack, velocity and some more influences. There is a static margin described for flare/fin stabilized projectiles for the relative position of CG and CP:

static margin B = ( (x_CP - x_CG)/length ) x 100%

For fin stabilized projectiles a steady state static margin of greater than 10% will keep it stable, couldn't really find what margin to use for flare stabilized projectiles but once CP goes in front of CG it will start tumbling. The relation in this is at least that the relative positions of CP and CG are critical to it's stability. (there are some very interesting papers on the internet about this but most are aimed at supersonic rockets/projectiles).

Based on this I also have a feeling that this has a lot to do with the stability of projectiles like the monster redesigneds, their CG is pretty far back so you need speed to push CP behind it with sufficient margin to keep it stable at distance.

I'm planning to make a request for more data on pellets so this is not only built on our local experiences and can be compared to others results. Would be nice to see if my estimations hold up with different conditions, height etc.
Click to expand...

Ahhhhh right! I totally forgot that you have access to an indoor range. 

What's the slowest barrel twist rate that you've tested with thus far? I did some experimentation recently with some 1:32" twist (choked) polygonal LW barrels at 100y using 18gr, MRDs and Beasts. 



Long story short, these barrels are absolutely incredible for shooting the 18gr and MRDs at high velocity (1010-1075), but I was surprised that the Beasts were so abysmal! I could see the precession spiraling when I reviewed the HEVC scope cam footage.

I thought the Beasts were similar (ballistically) to the MRDs, but they definitely seem to require a much faster twist rate than the MRDs to be stable. E.g., I've only been able to get them to group decently around 1000FPS in an un-choked CZ.


 
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Again I need to ask what happens when the twist rate is zero? Seems to me that water being 900 times as dense as air or they're about, it would be a simple experiment to drop a pellet into water and simply watch what happens. My theory is any drag stabilized projectile which is not spinning will remain stable at any subsonic velocity.

If that is the case your experiment reduces to the conclusion that no spin gives the longest stable flight for a drag stabilized projectile.
 
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The dynamic effects of wind, clipping etc are not taken into account here, this is about the destabilization that happens even in indoor conditions with practically no extra influences. With a couple of people we combined what we saw and measured (just like what bob mentioned) and based on that we started crunching numbers to see if we could find relations.
Click to expand...

What we basically saw was that twist rate and muzzle velocity had the biggest influence on influencing the downrange stability of a pellet. There is of course a difference between the different shapes of pellets so these graphs are custom to each pellet, muzzle velocity, twist rate, BC (which has a barrel dependency
1f605.svg
//www.w3.org/2000/svg%22%20viewBox=%220%200%20210%20140%22%3E%3C/svg%3E).

CG is basically determined by design and won't change as long as the pellet remains in the same shape and weight. CP will change depending on angle of attack, velocity and some more influences. There is a static margin described for flare/fin stabilized projectiles for the relative position of CG and CP:

static margin B = ( (x_CP - x_CG)/length ) x 100%

For fin stabilized projectiles a steady state static margin of greater than 10% will keep it stable, couldn't really find what margin to use for flare stabilized projectiles but once CP goes in front of CG it will start tumbling. The relation in this is at least that the relative positions of CP and CG are critical to it's stability. (there are some very interesting papers on the internet about this but most are aimed at supersonic rockets/projectiles).

Based on this I also have a feeling that this has a lot to do with the stability of projectiles like the monster redesigneds, their CG is pretty far back so you need speed to push CP behind it with sufficient margin to keep it stable at distance.

I'm planning to make a request for more data on pellets so this is not only built on our local experiences and can be compared to others results. Would be nice to see if my estimations hold up with different conditions, height etc.
Click to expand...

Ahhhhh right! I totally forgot that you have access to an indoor range. 

What's the slowest barrel twist rate that you've tested with thus far? I did some experimentation recently with some 1:32" twist (choked) polygonal LW barrels at 100y using 18gr, MRDs and Beasts. 



Long story short, these barrels are absolutely incredible for shooting the 18gr and MRDs at high velocity (1010-1075), but I was surprised that the Beasts were so abysmal! I could see the precession spiraling when I reviewed the HEVC scope cam footage.

I thought the Beasts were similar (ballistically) to the MRDs, but they definitely seem to require a much faster twist rate than the MRDs to be stable. E.g., I've only been able to get them to group decently around 1000FPS in an un-choked CZ.

Click to expand...

The slowest twist I've tested is with 1:24, haven't used a 1:30/32 yet. Might buy one sometime but at the moment enough things to test on other subjects 😅

The beast are really close to slug shape so I guess you should look more into that direction in terms of twist needs indeed.
 
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Again I need to ask what happens when the twist rate is zero? Seems to me that water being 900 times as dense as air or they're about, it would be a simple experiment to drop a pellet into water and simply watch what happens. My theory is any drag stabilized projectile which is not spinning will remain stable at any subsonic velocity.

If that is the case your experiment reduces to the conclusion that no spin gives the longest stable flight for a drag stabilized projectile.
Click to expand...

If I extrapolate the graph to zero twist it most likely ends up at a downrange destabilisation speed of around 0 m/s. It's also hard to get nutation with zero spin, precession can be possible but I haven't used barrels with no twist. If you can arrange one we can give it a try 😁

Pellets aren't exactly drag stabilized, the skirt is not wide or long enough to consider it as a drag surface for stabilizing. It's called flare stabilized what pellets use.
 
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