Wind Drift formula

[User4302021]

It comes down to practice and a lot of bullets down range to learn your holds and why you like to do.

The math is the math. It doesn't change, and it doesn't have to be a mystery.

Have an actual plan, learn the math, learn to judge wind.

An ill prepared shooter could go out and shoot case after case of ammo in the blind, and never learn what a casual student with a little training and knowledge can pick up relatively quickly.

 

[User4302021]

I have to sit down with the ballistic calculator set to 100 yard increments and just play with the wind

I usually find in mils that out to 600 ish I can say something like .1 mil per 100 yards per 4mph of of wind. But... Once I cross to about 700 yards then the slowing of the bullet kicks in and I may need to start adding an extra .1 per hundred in addition.
So at 4mph
100 yards .1mil
200 yards .2 mil
300 yards .3 mil
400 yards .4 mil
500 yards .5 mil
600 yards .6 mil
700 yards .8 mil
800 yards 1.0 mil

You will also find that the first number of a g1 ballistic coefficient will be a good number to start with

The BC method you are referring to assumes a bullet at 2,800 fps at 2,000 ft elevation.

Adjustments have to be made for speed and altitude.

If you are adding .1 after 600 yards, then your bullet is not a "4", it is a"3.5". Probably because you are either at sea level, or you are only going 2,700 fps or less.

 

[Plinkit]

The BC method you are referring to assumes a bullet at 2,800 fps at 2,000 ft elevation.

Adjustments have to be made for speed and altitude.

If you are adding .1 after 600 yards, then your bullet is not a "4", it is a"3.5". Probably because you are either at sea level, or you are only going 2,700 fps or less.

Bullets have to slow down eventually... I'm at Sea level so mine slows pretty quick.

 

[Capt RB]

One I've been using for multiple rounds and works quite well is BC=mph for .1mil every 100yds full value. Frank has talked about this on his podcast a few times. It is more than good enough for steel with no dope. Once your load is solid you can fine tune this a bit but most can't call the wind close enough. Best part is x2 x3 is simple as is .2.4.6 or .3.6.9 etc etc
Explains why the mil based scope is preferred for dynamic target shooting

 

[Canhunter35]

One I've been using for multiple rounds and works quite well is BC=mph for .1mil every 100yds full value. Frank has talked about this on his podcast a few times. It is more than good enough for steel with no dope. Once your load is solid you can fine tune this a bit but most can't call the wind close enough. Best part is x2 x3 is simple as is .2.4.6 or .3.6.9 etc etc
Explains why the mil based scope is preferred for dynamic target shooting

Left side of target or right side lol

Knowing your wind angles and how it'll react to ur environment is the hard part imo.

 

[Capt RB]

Left side of target or right side lol

Knowing your wind angles and how it'll react to ur environment is the hard part imo.

I like to shoot in light snow to determine my base for wind angle. The range I do alot of work on has a 7 to 11 as it rises and falls for the normal weather pattern. If I can shoot in north east winds it will come from the right side of our range. This also will show a 2 to 4 or 1 to 5 effect as it rises and falls. This is because of the the mandated berms. It really helps build a good book for a rifle. It's not always pleasant however it has served me well for years

 

[Canhunter35]

I like to shoot in light snow to determine my base for wind angle. The range I do alot of work on has a 7 to 11 as it rises and falls for the normal weather pattern. If I can shoot in north east winds it will come from the right side of our range. This also will show a 2 to 4 or 1 to 5 effect as it rises and falls. This is because of the the mandated berms. It really helps build a good book for a rifle. It's not always pleasant however it has served me well for years

Yeah the berms can really alter the wind, I've been bamboozled by coulees and the funnelling effect they can have wind more than a few times

 

[Tangent]

One I've been using for multiple rounds and works quite well is BC=mph for .1mil every 100yds full value. Frank has talked about this on his podcast a few times. It is more than good enough for steel with no dope. Once your load is solid you can fine tune this a bit but most can't call the wind close enough. Best part is x2 x3 is simple as is .2.4.6 or .3.6.9 etc etc
Explains why the mil based scope is preferred for dynamic target shooting

With today's available technology, the G1 coefficient method is out-dated IMO. There are a lot of assumptions that go into this 'method' but my understanding is that it was based on a 0.308 at moderate velocities at moderate density altitude. It does kinda-sorta gets you close for a fair amount of cartridges, but there's just better methods now.

Using JBM, Hornday 4DoF, etc., you can back-out your 'wind-number' for your specific rifle/ammo combo and use it for mil-radian, MOA, IPHY, etc.

 

[Capt RB]

With today's available technology, the G1 coefficient method is out-dated IMO. There are a lot of assumptions that go into this 'method' but my understanding is that it was based on a 0.308 at moderate velocities at moderate density altitude. It does kinda-sorta gets you close for a fair amount of cartridges, but there's just better methods now.

Using JBM, Hornday 4DoF, etc., you can back-out your 'wind-number' for your specific rifle/ammo combo and use it for mil-radian, MOA, IPHY, etc.

I use the method I use because it works for me with the loads I use it with. Just because something is older doesn't mean it doesn't work well. I still mil targets shoot and then check with my lrf. The use of tech is great however being able to make a shot without it at distance consistently speaks volumes for the shooter because he/she had to learn by putting in the time to acquire the skill rather than buy it

 

[TexSavage]

What about Jeff Hoffman's formula for those of us that use MOA? I found the linked document an interesting read. I shoot a 300WSM with the Berger 215 @2800fps and my windage looks to be about .5 to .55 of his value for the .308 round he uses as a base of 1 for his formula. I'm going to try and get over the next several weeks and maybe get some real fire testing of his formula. Of course a small 10mph wind here in the panhandle of Texas would be a pipe dream! Here's the link I found for it:

http://www.millettsights.com/downloads/JeffHoffmanWindFormula.pdf

 

[JLM8401]

I watch the video today explaining a wind drift formula. It said that the constant of a .308 ranged from 10 to 14. What is the constant for a 6.5 Creedmoor and how do you come up with these numbers.

I did this sometime ago. I don't have it with me but I believe it was in the 17 range at 800 yards. Ill look and post.

 

[Tangent]

I use the method I use because it works for me with the loads I use it with. Just because something is older doesn't mean it doesn't work well. I still mil targets shoot and then check with my lrf. The use of tech is great however being able to make a shot without it at distance consistently speaks volumes for the shooter because he/she had to learn by putting in the time to acquire the skill rather than buy it

My only point is the G1 method is a swag, which can easily lead to a 'tail wagging the dog scenario'. You can find yourself adjusting a wind call to match the swag'd drift. And the G1 method is not very applicable to fast moving high BC projectiles that are favored for long range hunting.

The computing power at your fingertips right now dwarfs the capabilities available at the time the G1 method was established. For me, better is better....and it's free....and you don't need to rely on it every shot....but to each their own.

 

[User4302021]

My only point is the G1 method is a swag, which can easily lead to a 'tail wagging the dog scenario'. You can find yourself adjusting a wind call to match the swag'd drift. And the G1 method is not very applicable to fast moving high BC projectiles that are favored for long range hunting.

The computing power at your fingertips right now dwarfs the capabilities available at the time the G1 method was established. For me, better is better....and it's free....and you don't need to rely on it every shot....but to each their own.

You don't really understand the method at all.

It is called the BC method because the first number of the G1 BC closely approximates the wind that will give you 0.1 MIL drift per 100 yards. A better nomenclature would be the MIL method (the wind that gives 1 MIL drift at 1K yards).

When properly calculated, this method will keep you to within 0.1 MILs at all yard lines to 1K, (or within a rounds supersonic range). I use it for 223, all the way up to 338AX.

The G1 number lines up with a projectile traveling 2,800 fps at 2,000 ft elevation.

If your bullet is 200 fps faster, your 5 mph bullet (.500 G1) will be a "6".

If your bullet is 200 fps slower, your 5mph bullet will be a "4".

4,000ft of positive elevation change, and your 5mph bullet becomes a "6".

At sea-level, it changes from "5" to "4.5".

When the Army wrote this method into the newest sniper manual, even they failed to understand the effects of velocity and altitude. That is why they are wrong in the manual.

If you are fingering an app to tell you your drift, you are already behind the curve. What are you gonna do when your phone dies, or freezes, or shuts down from over heating? It just isn't that hard.

 

[Tangent]

You don't really understand the method at all. It is called the BC method because the first number of the G1 closely approximates the wind that will give you 0.1 MIL drift per 100 yards. A better nomenclature would be the MIL method (the wind that gives 1 MIL drift at 1K).

When properly calculated, this method will keep you to within 0.1 MILs at all yard lines to 1K, (or within a rounds supersonic range). I use it for 223, all the way up to 338AX.

The G1 number lines up with a projectile traveling 2,800 fps at 2,000 ft elevation.

If your bullet is 200 fps faster, your 5 mph bullet (.500 G1) will be a "6".

If your bullet is 200 fps slower, your 5mph bullet will be a "4".

4,000ft of positive elevation change, and your 5mph bullet becomes a "6".

At sea-level, it changes from "5" to "4.5".

When the Army wrote this method into the newest sniper manual, even they failed to understand the effects of velocity and altitude. That is why they are wrong in the manual.

Ha! Sounds like Army snipers could really use a consult from you to learn how to shoot!

I fully understand how the method works, but the FACT is that the method cannot be uniformly applied to all projectiles at all velocities, at all Density-Altitudes without clumsy step-function type corrections. Plus the method only works with a specific angular unit.

But you like what you like...so rock on brother.