Wind Drift vs Velocity by BC

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Here is a little "notional" study I did three or four years ago. It was the result of a conversation I had with Mr. Sterne over on AGG. The data is self-explanatory. Maybe someone will find it useful or food for thought.

wind-drift-bc-velocity.1614627603.jpg


This post had gone quietly into the night when it was resurrected. I made this table probably some time around 2015 or 2016. I don't really remember. There are a number of things you can discover from it but the most useful aspect of the table is the fact that you can extrapolate your wind drift if you know your range, muzzle velocity, and pellet BC. Let me do an example.

Suppose you are shooting at 60 yards, wind is 10 mph at 2 o'clock (half value), muzzle velocity is 770 fps and BC is 0.24. Look at the chart for the nearest range, nearest velocity, and nearest BC. For 50 yards, 800 fps and 0.02 BC I see drift is 2.84". Ok we are (60/50) further, we are (770/800) on velocity, and (0.24/0.20) on BC. Crunch those numbers and we are 20% further, 96% as fast and we are 20% slipperier. That means increase drift by 20%, decrease that number by 4% and then increase the result by 20%.

That looks like this ((2.84*1.2)*0.96)*1.02) put that in your calculator and you get about 3.9" of drift. Now then this is a 10 mph wind so you have to double the drift BUT it is at 2 o'clock and that's a half value direction. The quick and dirty is hold for 4 inches of wind. There are better ways to do it but they involve a lot more addition and subtraction and this is for FIELD use anyway.
 
Very interesting, thanks for the chart! 😊



I'd think that different projectiles with different forms/ shapes would have a little different behavior. Like this:

🔸A more aerodynamically shaped projectile like a dome would probably experience the marked increase in drag (—> decrease in BC) at higher velocities (850-950fps, moving into transonic speed) —

🔸whereas an less aerodynamically shaped wadcutter would suffer that big increase of drag much sooner (say 700fps). 





🔶Also, based on a chart that shows how BC (really: drag) varies with velocity that Bob Sterne over at GTA published, it seems that heavier domed pellets suffer the drag increase at higher velocities than lighter domes.



I'll attach Bob's chart, that is based on a series of tests he's done with JSB domes.



Matthias



❌ Attachment: Variable BC numbers for JSB Domes .22cal

PELLET BC. For JSB Series, .22cal. By Bob Sterne 2017.1614694674.jpg

 
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Also, it seems that those doing the most research are concluding that the available drag models most often used for air guns are lacking in describing slug behavior. Maybe the new differently shaped heavy pellets are somewhere between diabolo pellets and slugs in aerodynamic behaviour and sit in an area of the "model" that isn't perfectly accurate. Maybe...?
 
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You usually get your best BC somewhere between 800 and 900 and probably a smoother shot cycle than these guys shooting in the 900's.
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Yes you do. There is a sweet spot between the velocity and BC which minimizes wind drift. The interesting dynamic working here is the tradeoff between three values. They are velocity, accuracy, and drift. Seems like the sweet spot for most round nosed pellets is about 850 fps.
 
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Very interesting, thanks for the chart! 😊



I'd think that different projectiles with different forms/ shapes would have a little different behavior. Like this:

🔸A more aerodynamically shaped projectile like a dome would probably experience the marked increase in drag (—> decrease in BC) at higher velocities (850-950fps, moving into transonic speed) —

🔸whereas an less aerodynamically shaped wadcutter would suffer that big increase of drag much sooner (say 700fps). 





🔶Also, based on a chart that shows how BC (really: drag) varies with velocity that Bob Sterne over at GTA published, it seems that heavier domed pellets suffer the drag increase at higher velocities than lighter domes.



I'll attach Bob's chart, that is based on a series of tests he's done with JSB domes.



Matthias



❌ Attachment: Variable BC numbers for JSB Domes .22cal

PELLET BC. For JSB Series, .22cal. By Bob Sterne 2017.1614694674.jpg
Click to expand...


That chart is the one that I found while I was working on the spread sheet. It led to the conversation between Bob and I over on AGG. He confirmed my suspicions. Since he had already done the work I never did upload the SS output. Then I found it the other day and thought it might be a good topic for newer members. Bob is a treasure, for sure.
 
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Also, it seems that those doing the most research are concluding that the available drag models most often used for air guns are lacking in describing slug behavior. Maybe the new differently shaped heavy pellets are somewhere between diabolo pellets and slugs in aerodynamic behaviour and sit in an area of the "model" that isn't perfectly accurate. Maybe...?
Click to expand...


The thing about BC models is that they are always an approximation unless you happen to be shooting the only projectile in existence that perfectly fits your model on a perfect day at a perfect elevation above sea level ... =)

G1 is good for flat based spitzers and that fits most AG slugs unless they have huge hollow points and/or a large meplat. GA is good for diabolo pellets.

Most of the models are pretty darn good from a practical shooting perspective. They are generally better than anyone can shoot without a machine rest indoors.
 
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Also, it seems that those doing the most research are concluding that the available drag models most often used for air guns are lacking in describing slug behavior. Maybe the new differently shaped heavy pellets are somewhere between diabolo pellets and slugs in aerodynamic behaviour and sit in an area of the "model" that isn't perfectly accurate. Maybe...?
Click to expand...

I've experimented with this for the past two years with various slugs and have decided to NOT use the G1 profile for airgun slugs. Instead I use the RA4 profile for .22 Rimfire type bullets. Seems to work more accurately once out past 135 to 140 yards. Up to that point they (G1 and RA4) are very similar. I also have been using the G1 profile for the more ballistic pellets such as the .22 Monster RDs and the .25 Exact Heavy instead of the more common GA pellet profile. For lower BC pellets such as the .22 JSB Heavy 18.1 or the .30 JSB Exact 44.75 I still use the GA profile...
 
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Also, it seems that those doing the most research are concluding that the available drag models most often used for air guns are lacking in describing slug behavior. Maybe the new differently shaped heavy pellets are somewhere between diabolo pellets and slugs in aerodynamic behaviour and sit in an area of the "model" that isn't perfectly accurate. Maybe...?
Click to expand...

I've experimented with this for the past two years with various slugs and have decided to NOT use the G1 profile for airgun slugs. Instead I use the RA4 profile for .22 Rimfire type bullets. Seems to work more accurately once out past 135 to 140 yards. Up to that point they (G1 and RA4) are very similar. I also have been using the G1 profile for the more ballistic pellets such as the .22 Monster RDs and the .25 Exact Heavy instead of the more common GA pellet profile. For lower BC pellets such as the .22 JSB Heavy 18.1 or the .30 JSB Exact 44.75 I still use the GA profile...
Click to expand...

Sounds like similar results to what I had recently read. Thanks for the information. I'm not a "calculator" and don't use programs but the topic interests me, particularly the apparent volatility in the traditional estimations. 
 
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@bandg I agree. However, I can always tell when someone doesn't go long range (greater than 100 yards) hunting because they say they don't use a "calculator". Shooting targets or spinners long range can be done without a ballistics app, since you have plenty of time and ammo for ranging and sighting in prior to actually hitting the targets. When hunting you need to laser range the target, adjust your scope (or holdover) and take the shot. Without a good laser rangefinder and ballistics app like Strelok you're doomed to failure... This assumes you've taken the time to verify proper parameters in your app like slug speed, scope height, BC, etc. 
 
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Bob Sterne over at GTA just published another article in HardAir Magazine on slug ballistics and BC.

He's been working with Miles Morris, a professional ballistician who made his career designing huge military projetiles — and working on the ballistics of airgun pellets/slugs! 😄 Very cool, indeed. 👍🏼



🔶 Anyhow, he did some calcs to show how our current AG slugs are not a good match for either the G1 or GA drag models — when above 800fps.

🔶 Our current hollow point slugs with their fairly large meplat have less drag between 800 and 950fps (0.8—0.95 mach) than the G1 and the GA drag model assumes. But beyond 950fps our AG's slug's drag increases more than assumed in the G1 and GA model.



🔶 So, if we measure our BC and happen to take measurements V1 at say 950fps at the muzzle and V2 at say 800fps, using a ballistic calculator and the G1 or GA model will calculate us a higher BC than our slugs actually deliver.



🔶 It also explains why we can shoot slugs at somewhat higher velocities without getting penalized with a lowered BC when shooting domed pellets. 



The article is explorative, but I'm sure more Miles and Bob have more in store for us. ➔ Cool to have people like them move our sports forward! 😄👍🏼



Matthias



❌ Article link:

https://hardairmagazine.com/ham-columns/some-new-airgun-slug-drag-models-by-miles-morris/



Below one of the charts from the HardAir Magazine article:

BC of Slugs. Drag Model for Slugs with 65 Percent Meplat vs. G1 and GA Models. BY Miles Morris...jpg

 
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@bandg I agree. However, I can always tell when someone doesn't go long range (greater than 100 yards) hunting because they say they don't use a "calculator". Shooting targets or spinners long range can be done without a ballistics app, since you have plenty of time and ammo for ranging and sighting in prior to actually hitting the targets. When hunting you need to laser range the target, adjust your scope (or holdover) and take the shot. Without a good laser rangefinder and ballistics app like Strelok you're doomed to failure... This assumes you've taken the time to verify proper parameters in your app like slug speed, scope height, BC, etc.
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Correct in that I don't hunt anymore. At short or long range. But if I were to want to hunt at ranges over 100 yards, it almost certainly wouldn't be with any of my air guns. Also, I would venture a guess that I've spent as much time hunting in decades past as most anyone here so I do have some past experience. However, I disagree absolutely completely on the NEED for any program. What do you think a ballistic program can provide that actual shooting cannot? As you note, range the target and take the shot. If you are using the "calculator" at that time then something is very wrong. And If you've shot very much for the intention of hunting then you should know the trajectory of your round out to any truly effective distance. If so, then it seems a "program" can supply little additional to that knowledge. And if not, a shot should not be taken. And with actual shooting, you have actual verified information, not an estimate. We'll have to agree to disagree on this concept entirely.
 
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Concur. We can agree to disagree. When there is more than a targets height drop every couple of yards its hard to judge the exact drop without a good range card. And using a ballistics app makes it infinitely easier to generate a good range card compared to putting out targets every two yards from 50 to 250 yards. Could that be done? Of course. Who does it? No one I know. The drop with a high BC .25 slug differs by 4 inches between 175 and 180 yards. And it gets much larger the farther out you go. More power to those that can remember their scope dope every two yards out to 200+ yards. I don’t have that brain power and use my ballistic app to generate an accurate range card that can be verified at a few different yardages. No offense @bandg 


 
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Concur. We can agree to disagree. When there is more than a targets height drop every couple of yards its hard to judge the exact drop without a good range card. And using a ballistics app makes it infinitely easier to generate a good range card compared to putting out targets every two yards from 50 to 250 yards. Could that be done? Of course. Who does it? No one I know. The drop with a high BC .25 slug differs by 4 inches between 175 and 180 yards. And it gets much larger the farther out you go. More power to those that can remember their scope dope every two yards out to 200+ yards. I don’t have that brain power and use my ballistic app to generate an accurate range card that can be verified at a few different yardages. No offense @bandg 

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Definitely no offense taken. Seems to be a good discussion. I've just never viewed the information from the programs as consistently reliable. Always seemed too dependent on specific inputs. I certainly could be wrong and I'm absolutely not a tech person. Could well be my loss. I don't shoot my airguns at ranges such as you mention but I think windage would be more of a problem than drop at such distances. I do shoot firearms out to 600 yards regularly and that certainly is the case in that realm-compensating for wind is more complex and wind causes a lateral miss more often than an incorrect drop correction causes a vertical miss.
 
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Help me understand this.....circles added for the specific example, although the trend seems to be throughout all the data here.



drift.1627426331.jpg


Is this saying that a pellet with a better BC will drift less? 

Was just reading elsewhere that BC tells us absolutely NOTHING about the wind drift characteristics of the projectile except in head and tail winds but in this chart it seems to show that a 5mph wind at 3 oclock wreaks havoc on that 0.01 BC pellet impact point at 100 yards, pushing it 23 more inches than the 0.04 bc pellet, when both start at 900fps.

Don't know what's more frustrating, an inaccurate and inconsistent gun, or coming to AGN to learn and finding inaccurate and inconsistent information. 
 
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Help me understand this.....circles added for the specific example, although the trend seems to be throughout all the data here.



drift.1627426331.jpg


Is this saying that a pellet with a better BC will drift less? 

Was just reading elsewhere that BC tells us absolutely NOTHING about the wind drift characteristics of the projectile except in head and tail winds but in this chart it seems to show that a 5mph wind at 3 oclock wreaks havoc on that 0.01 BC pellet impact point at 100 yards, pushing it 23 more inches than the 0.04 bc pellet, when both start at 900fps.

Don't know what's more frustrating, an inaccurate and inconsistent gun, or coming to AGN to learn and finding inaccurate and inconsistent information.
Click to expand...


I made that chart.
 
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My friends,

let's not get this thread also shut down. 😊

I found the discussion on the thread I posted rather interesting — before we drifted off into something less airgunny....



Let's move on to things that will help airgunning. 👍🏼

One suggestion: Help airgunners make a gun purchase or tuning decision of how much power they want in a gun and what caliber.

To make an informed decision we could offer them charts that show how beneficial additional power truly is to (1) increase point blank range, (2) offset typical ranging errors, and (3) offset wind drift of typical wind estimation errors. All these charts would differentiate between typical calibers (and using typical quality, high BC pellets).



Peace, 😊

Matthias
 
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