❓ Suited-for-the-barrel Pellets Perform Badly in the Wind? WHY? HOW?

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JungleShooter

JungleShooter

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Suited-for-the-barrel Pellets Perform Badly in the Wind? WHY? HOW? ❓



Maybe I should explain:

(1)

So, we know that each barrel "likes" certain pellets.



(2)

So we test a bunch of pellets to find the "magic pellet" for our barrel — the suited-for-the-barrel pellet. 

We do the testing in near perfect conditions, because if we did it with wind gusting our precision results would get messed up by the wind.



(3)

Then, we shoot those suited-for-the-barrel pellets in normal conditions — with WIND.

➔ Now, people have reported occurences where those barrel-suited pellets actually do not shoot good in the wind.

➔ W-T-H?!?

("do not shoot good" refers to group size — not the amount of wind drift — let's assume that the comparison is between pellets of similar BC — since comparing a wadcutter with a dome at 50y in the wind would be pointless.)





❓ I'm puzzled! WHY is this? HOW can this be? 🤔

Matthias





Here is just one report of such an occurrence, and I have read a fair share over the years:

https://www.airgunnation.com/topic/yrrah-pellet-rolling-does-it-work-a-study/#post-1051349
 
Case in point of doing some testing of late in the Taipan Vet .177

Using this rifle to try it out as a Field Target rig and found "Accuracy Wise" the JSB Monster 13.4 weight pellets shot the best at > 20 fpe power limits.

The Original Straight waist AkA: trash cans accurate as they are MOVED like crazy in the wind being shot at @ 815 fps .. Bummer !!

The Newer "Redesigned" monsters which appear to shoot with the same BC value DON'T MOVE around nearly as much in the wind at the same speed ... Go figure ?





SIDE PROFILE and AREA presented to the wind is very likely the reason IMO.



Scott S
 
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Case in point of doing some testing of late in the Taipan Vet .177

Using this rifle to try it out as a Field Target rig and found "Accuracy Wise" the JSB Monster 13.4 weight pellets shot the best at > 20 fpe power limits.

The Original Straight waist AkA: trash cans accurate as they are MOVED like crazy in the wind being shot at @ 815 fps .. Bummer !!

The Newer "Redesigned" monsters which appear to shoot with the same BC value DON'T MOVE around nearly as much in the wind at the same speed ... Go figure ?





SIDE PROFILE and AREA presented to the wind is very likely the reason IMO.



Scott S
Click to expand...

Thanks Scott, that was what I was mulling around in my head. That side profile catches the wind. The pellet is accelerated laterally more quickly (just exactly like a sail boat).

By the way, I studied that pelseat image you posted a while back and have to say I reversed my opinion. That is a very good design and you might consider marketing it (or maybe building a 3d template of it for printers and printing them of something like PETG).
 
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Post rifling effect on the pellet plays a part too. Pellet leaving a 12 land and groove barrel has a lot more edges and angles on its surface to catch air molecules, or more specifically, moving and turbulent air molecules (read: WIND). Think blades on fans and propellers, you want to either catch a lot of energy (windmill) or push/pull against water or air (propellers) than the blades are larger/more aggressive. Same thing with pellets, one that goes through a polygonal barrel and has hardly any sharp edges/fins on it will slip through the air better than one that goes through a 12 land and groove barrel. 

Although, theoretically, the BC is supposed to be the collective fudge factor that accounts for the amalgamation of all of these influences and their net effect on how well a projectile maintains its intended/desired flight path. 

The concept of ballistic coefficient isn't perfect but seems to be the best we've got as a way of quantifying a projectiles ability to retain energy/combat deflection. 

A relatively "good" or "bad" BC is usually reflected in actual pellet performance. (Ie a higher BC pellet will perform better than a lower BC pellet). 
 
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Remember — we are comparing pellets of similar BC....



If we compared a low BC wadcutter with a high BC dome, of course the dome would have less drift.... 😊



We are not comparing drift, but group size — at least that's what I thought the forum posts were talking about, e.g.:

The group size of Pellet A and Pellet B WITHOUT wind is the same, they are suited for the barrel.

The BC of Pellet A and Pellet B is aprox. the same.

Shooting A and B WITH wind the group size of Pellet A is significantly larger than the group sizes of Pellet B.



Matthias
 
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Large group size in the wind IS drift. Sidewinds, headwinds ,tailwinds and every other 360 degree combination of such cause a pellet to drift, up, down, left, right, diagonally. And the overall group size is larger when all those various wind effects on each pellet causes them to drift away from aim point. 

Some pellets/barrel combos just don't shoot well in the wind....

The concept you're getting at here is that sometimes BC isnt the whole story, as I brought up a few months ago and you disagreed. If two BCs can be nearly identical, and both pellets shoot similarly accurately in no wind, but one shoots larger groups when there's wind than the other one, well then, our concept of BC simply isn't reflecting all of the factors. 

BC as a functional tool for predicting the ease at which precision can be obtained is pretty good, but not perfect. 
 
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By the way, I studied that pelseat image you posted a while back and have to say I reversed my opinion. That is a very good design and you might consider marketing it (or maybe building a 3d template of it for printers and printing them of something like PETG).
Click to expand...



That image IS NOT one of a pellet seater, but one that is of a TOOL that accurately Trues up and Straightens out a pellets skirt profile. Each tool is make for a specific pellets skirt tail angle, depth and diameter / caliber.

For if a pellets skirt DOES NOT fold in evenly as it loads into barrel, YAW is created and pellet will wobble all the way down barrel and fly weird all the way to POI.

This is for most AG shooters EXCESSIVELY NEUROTIC .... agreed, but for those who want the highest consistency potential another trick in ones hat that may for some shooters make a difference ? * This tool IS NOT a flaring devise !!!!!!!!!

DSCF0548_50.1627239799.jpg
DSCF0549_50.1627239812.jpg
DSCF0550_50.1627239823.jpg
DSCF0551_50.1627239835.jpg
DSCF0552_50.1627239854.jpg

 
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Large group size in the wind IS drift. Sidewinds, headwinds ,tailwinds and every other 360 degree combination of such cause a pellet to drift, up, down, left, right, diagonally. And the overall group size is larger when all those various wind effects on each pellet causes them to drift away from aim point. 

Some pellets/barrel combos just don't shoot well in the wind....

The concept you're getting at here is that sometimes BC isnt the whole story, as I brought up a few months ago and you disagreed. If two BCs can be nearly identical, and both pellets shoot similarly accurately in no wind, but one shoots larger groups when there's wind than the other one, well then, our concept of BC simply isn't reflecting all of the factors. 

BC as a functional tool for predicting the ease at which precision can be obtained is pretty good, but not perfect. 
Click to expand...

BC is not intended to have ANY relationship what so ever to wind drift or accuracy. BC is a number (actually a coefficient) you plug into a ballistics equation to adjust the drop of a projectile relative to the projectile being modeled by the equation.

https://www.police1.com/police-products/firearms/articles/ballistics-101-what-is-ballistic-coefficient-fRDCeuu1pkmFQKu1/

It does not predict precision. It predicts rate of drop relative to a model projectile.
 
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By the way, I studied that pelseat image you posted a while back and have to say I reversed my opinion. That is a very good design and you might consider marketing it (or maybe building a 3d template of it for printers and printing them of something like PETG).
Click to expand...



That image IS NOT one of a pellet seater, but one that is of a TOOL that accurately Trues up and Straightens out a pellets skirt profile. Each tool is make for a specific pellets skirt tail angle, depth and diameter / caliber.

For if a pellets skirt DOES NOT fold in evenly as it loads into barrel, YAW is created and pellet will wobble all the way down barrel and fly weird all the way to POI.

This is for most AG shooters EXCESSIVELY NEUROTIC .... agreed, but for those who want the highest consistency potential another trick in ones hat that may for some shooters make a difference ? * This tool IS NOT a flaring devise !!!!!!!!!

Click to expand...

Yes I caught that after I posted. But that is what I intended. I've been experimenting with those lately and I am coming to the conclusion that you came to... you want to make the skirt round but NOT flare it.

That yaw you are talking about is what I've been noticing. It would be tough to make one for every pellet out of metal but making them on a 3d printer would be efficient enough to make it profitable (to my mind).
 
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@cornpone, 

BC predicts precision ≠ "BC is a functional tool for predicting the ease at which precision can be obtained"

Every shot sent downrange is a combination of inherent accuracy/inaccuracy of a projectile and the gun it's being fired from, shooter ability to squeeze the trigger at the correct time and place, as well as shooter ability to assess the wind conditions at the time of trigger break and adjust accordingly. With diabolo pellets at long ranges, that wind reading skill becomes paramount to precision (causing the pellet to impact @desired location). So, a pellet that resists deflection/retains it's energy better gives more room for error for the shooters ability/inability to accurately assess the microconditions present for the shot. So, a high BC pellet that resists deflection/speed decay is easier for the shooter to place in its desired downrange location.

And yes, BC is a measure of a pellets resistance to air molecules, both static (simply the presence of our atmosphere) and any currents within that atmosphere (WIND). 

What exactly do you think is making that pellet slow down (the "drop" to which you refer)? 

In more simple terms, ballistic coefficient is simply how slippery a pellet is as it passes through the atmospheric conditions present in its flight path. 

In even more simple terms, BC is a measure of how good a pellet flys through the air in specific conditions, compared to a different pellet flying through the air in whatever conditions present for its flight. 
 
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Sadly when these @ 5 different tools were made for those pellets being shot, it was done as a ONE OFF exercise on the metal lathe.

Paying no attention to actual Degree's, the compound was bumped progressively, cuts made until such time the angles matched each pellet type & caliber by FIT and not a measured or documented angle. The TIP of the taper BLUNTED to be JUST SHY of contacting the floor of the pellets skirt cavity. 

In using said tool, push too hard creating a flair the tool bottoms out preventing it. Like stated .... NEUROTIC endeavor absolutely !!



Scott S





PS ....

SORRY for side tracking the OP's original conversation ... My bad !
 
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@cornpone,

In even more simple terms, BC is a measure of how good a pellet flys through the air in specific conditions, compared to a different pellet flying through the air in whatever conditions present for its flight.
Click to expand...

Then basically we are saying the same thing. Drop is a function of time of flight. Time of flight is a function of drag. BC is a number used to relate drag of the pellet under consideration to a SPECIFIC drag model. BC for a specific pellet is not the same when using say G1 and GA, for example. You know this.

It has nothing at all to do with predicting accuracy (if you define accuracy as group size). I've got lots of pellets I can shoot in my rifle. I pick the one with the best accuracy as measured on a target, not the one with the "best" BC. Now then I do start my tests with the one with the best BC because I want accuracy at range. 

I think the points made here about wind drift being probably influenced by the cross section (from the side) are pretty important. Sure BC gets you less time in the air. But one pellet might have a BC of 0.04 but a 25% bigger side cross section than say a pellet with a BC of 0.03. Both are reasonable BCs but it is likely the one with the largest cross section (again from the side) is going to have more wind drift. It is a hard problem. Maybe we need something like a BC for the side section of pellets to use when computing wind drift. We have the computing power to do such things now.

BC is important but it doesn't tell you how accurate a pellet is going to be or how much wind drift you are going to experience. It is a good starting point. Yes drift is a function of time of flight and time of flight is a function of BC. Sadly none of the equations I have ever seen take into consideration cross section ... and it is unlikely any ever will because BC does "good enough" when calculating time of flight and time of flight tends to swamp those equations.

We both understand what we are talking about here, so we should be able to agree that the pellet with the best BC is not ALWAYS the pellet which bucks the wind best. Hopefully we can also agree that that is a particularly difficult problem. It would be very hard to document and harder still to simulate in the equations. Kind of like spin drift and Coriolis effect. The one is fairly easy to predict from BC (Coriolis) the other is better measured after you subtract out Coriolis and compensate for wind... Clearly there is a level of precision here which becomes "compulsive" ... as Scott suggests...
 
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Post rifling effect on the pellet plays a part too. Pellet leaving a 12 land and groove barrel has a lot more edges and angles on its surface to catch air molecules, or more specifically, moving and turbulent air molecules (read: WIND). Think blades on fans and propellers, you want to either catch a lot of energy (windmill) or push/pull against water or air (propellers) than the blades are larger/more aggressive. Same thing with pellets, one that goes through a polygonal barrel and has hardly any sharp edges/fins on it will slip through the air better than one that goes through a 12 land and groove barrel. 

Although, theoretically, the BC is supposed to be the collective fudge factor that accounts for the amalgamation of all of these influences and their net effect on how well a projectile maintains its intended/desired flight path. 

The concept of ballistic coefficient isn't perfect but seems to be the best we've got as a way of quantifying a projectiles ability to retain energy/combat deflection. 

A relatively "good" or "bad" BC is usually reflected in actual pellet performance. (Ie a higher BC pellet will perform better than a lower BC pellet).
Click to expand...

I have to agree about the number of lands and also add something about the twist rate and length. FX figured this out with smooth twist, as did some custom makers as well.. RTI has different twist rates for each caliber. Less rotation of a drag stabilized projectile is better in the wind. The diabolo shape wants to correct itself in flight and excessive spin works against it by creating a higher and lower pressures above or below, depending on twist direction and wind direction. With a rh twist and a r to l wind, the top edge of the pellet has more resistance than the bottom, and during a l to r wind the bottom edge will have more resistance. A 12” and 24” barrel with the same twist rate, velocity and pellet bc will not perfom the same in wind. Likewise, 2 barrels of the same barrel length, pellet, and velocity but with a 1:22 twist vs a 1:16 will also have different wind characteristics. If anyone plays disc golf, they can literally see what happens if they throw a disc L handed and R handed and watch the disc fall out of flight. It follows the spin because of the leading edge. 
 
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Post rifling effect on the pellet plays a part too. Pellet leaving a 12 land and groove barrel has a lot more edges and angles on its surface to catch air molecules, or more specifically, moving and turbulent air molecules (read: WIND). Think blades on fans and propellers, you want to either catch a lot of energy (windmill) or push/pull against water or air (propellers) than the blades are larger/more aggressive. Same thing with pellets, one that goes through a polygonal barrel and has hardly any sharp edges/fins on it will slip through the air better than one that goes through a 12 land and groove barrel. 

Although, theoretically, the BC is supposed to be the collective fudge factor that accounts for the amalgamation of all of these influences and their net effect on how well a projectile maintains its intended/desired flight path. 

Click to expand...




I was thinking about that too, definitely plausible. Would be cool to get 2 barrels side up side by side shooting same speed with same ammo in the same wind and see if the sharp edges indeed any any effect at all. 
 
Upvote 0
Post rifling effect on the pellet plays a part too. Pellet leaving a 12 land and groove barrel has a lot more edges and angles on its surface to catch air molecules, or more specifically, moving and turbulent air molecules (read: WIND). Think blades on fans and propellers, you want to either catch a lot of energy (windmill) or push/pull against water or air (propellers) than the blades are larger/more aggressive. Same thing with pellets, one that goes through a polygonal barrel and has hardly any sharp edges/fins on it will slip through the air better than one that goes through a 12 land and groove barrel. 

Although, theoretically, the BC is supposed to be the collective fudge factor that accounts for the amalgamation of all of these influences and their net effect on how well a projectile maintains its intended/desired flight path. 

Click to expand...




I was thinking about that too, definitely plausible. Would be cool to get 2 barrels side up side by side shooting same speed with same ammo in the same wind and see if the sharp edges indeed any any effect at all.
Click to expand...

This wasn't a perfect comparison, but check out the list titled "Wind Deflection:" on the second page, about 3/4 of the way down.

https://www.airgunnation.com/topic/bsa-gold-star-union-jack-in-177-ongoing-review/

Did a comparison between a couple barrels, one of which was the polygonal barrel in my field target gun that has proven to be exceptionally wind resistant. Measured BC was very similar but the meta-analysis of all the shots and how far they were from the aim point suggested that pellets leaving the poly barrel would get pushed less (horizontally) than pellets leaving a 12 land and groove barrel. 

Yes there were some flaws in the design of the comparison, but some data is better than completely unsupported claims. 
 
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Wind drift chart above is for Slugs. Pellets are the opposite.

I also see above many old wives tales about subsonic ballistics. For example, faster is better for wind drift because there’s less time for the wind to affect the pellet. WRONG. Or that BC has nothing to do with wind drift WRONG. Or “drift is a function of time of flight and time of flight is a function of BC.” WRONG again. 
And many others, but this has been beaten to death in the past. Just use the search to find older posts that will steer you in the right direction and away from the misconceptions. 

https://hardairmagazine.com/ham-columns/the-definitive-index-to-bob-sternes-ham-technical-articles/
 
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