Wind Drift formula

[User4302021]

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

Well, I learned from the guy that introduced it to the Army Sniper School at Ft. Benning back in the late 90's. If they didn't listen to him...they won't listen to me.

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.

It is exactly how your ballistic app does it, you just don't see the math.

Plus the method only works with a specific angular unit.

Actually the methodology works equally well with MOA. You just find your 5 MOA wind at 1K yards, and that gives you 1/2 MOA per 100 yards drift.

 

[Tangent]

Well, I learned from the guy that introduced it to the Army Sniper School at Ft. Benning back in the late 90's. If they didn't listen to him...they won't listen to me.

It is exactly how your ballistic app does it, you just don't se

Actually the methodology works equally well with MOA. You just find your 5 MOA wind at 1K yards, and that gives you 1/2 MOA per 100 yards drift.

Man, your kinda talking in a circle here. Using the G1 coefficient as a 'wind number' doesn't work on MOA or IPHY.

And ballistic calculators don't use step function type corrections.

What's funny is you've said:

You can use JBM Ballistics online, it's free and it works. Or use any other app you might have access to.

Now your trying to win an internet argument when I made a very similar statement to yours......ok man, YOU WIN

From now on, I'll look at the less applicable G1 model, proportion my velocity to 2,800 & proportion my altitude to 2000 to correct.....your right, much easier.

 

[User4302021]

Man, your kinda talking in a circle here. Using the G1 coefficient as a 'wind number' doesn't work on MOA or IPHY.

You don't follow so well. When I was talking about MOA, I used the word methodology. I never said you use the G1 for wind in MOA. You simply apply the same principles using a different number. That number is going to be approximately 50% greater than your G1 number.

What's funny is you've said:

Now your trying to win an internet argument when I made a very similar statement to yours......ok man, YOU WIN

From now on, I'll look at the less applicable G1 model, proportion my velocity to 2,800 & proportion my altitude to 2000 to correct.....your right, much easier.

Again, you don't follow so well. The OP had no interest in either system. He was looking for a way to derive a constant (which I provided). I then mentioned the MOA method of finding the 5 MOA base wind using JBM.

Using an app to find the base wind isn't any kind of violation of the method. No matter how the base wind is found, the relationship to the first number of the G1 BC is unchanged.

The main point is to know that base wind, and to be able to do it in your head when you are in the field instead of relying on a device. Then you can make instant adjustments based on what you see from second to second as the wind changes.

Basically, none of this discussion with you would be necessary if you hadn't started hacking on Capt RB over things you obviously don't understand as well as you thought.

I'm done. I'm tapping out.

 

[Plinkit]

Wind reading is not some perfect science to begin with...

So making a guess at what the collective wind value is across hundreds of yards is "SWAG" at the time....

I'll take something that gives me a close approximation quickly vs calculations that's going to take so long that the wind changes anyway

I am curious if you guys have gotten it down to a perfect science... how do you calculate all the wind differences across several hundred yards of terrain.... I've never seen perfectly consistent wind value across a flat open field... Let alone anything that has elevation changes, trees, etc

 

[User4302021]

@Plinkit, PM sent

 

[Deleted member 110997]

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

This is good

My recommendation is watch accuracy 1st videos until you understand them. As plinkit, use g1 bc. If at elevation 6k and up you don't need to add the .1 after 600

 

[Deleted member 110997]

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.

Hodnett's long wind formula is on point!

 

[Deleted member 110997]

Not sure

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.

Not sure what regular army uses but sof uses Hodnett's long formula.

 

[User4302021]

Not sure

Not sure what regular army uses but sof uses Hodnett's long formula.

Which is?

Todd Hodnett hadn't even heard about this method until sometime after 2005 when he started working for Horus.

It didn't stop him from claiming credit though.

 

[Deleted member 110997]

Which is?

Todd Hodnett hadn't even heard about this method until sometime after 2005 when he started working for Horus.

It didn't stop him from claiming credit though.

His method isn't the same as the simple bc method which came out in the 90s

Range x wind + wind+ constant

Or just get a tremor 3 reticle

Also, i call it the Hodnett's long formula, perhaps its called something else. Perhaps its Brian Litz formula or Horus formula or something else... most snipers from the .mil know it as Hodnett's. Because he taught it to me and at that time we were still using the antiquated formulas or the British rule of 9s for 308

In not long the wind reading laser system will be fielded and then all these awesome skills will dwindle as tech gives the ability for every shooter to have one....

I'm hearing some incredible things about the plastic compost casings....which to me carries zero logic but when sof snipers test it and have amazing results i cant argue that

 

[Tangent]

Like I said, using the first number of a G1 coefficient to determine a rifle's 'wind number' is not for me. Neither is a modified/tweaked/scaled version of the G1 method. But if that's what you're into, rock on (being serious). Most shooters have seen this, but the projectile pictured below is what the G1 model was based on:

That obviously does not look like any bullet that we shoot out of long range rifles, and the discrepancy is why I would prefer not to use a scaled version of that G1 projectile for much of anything that is considered 'long range'. Why would we move towards G7 models and then custom models for elevation (which is considered the easy part), and then default to an obsolete G1 model for wind (which is considered the hard part)?

 

[Deleted member 110997]

Yes but

Like I said, using the first number of a G1 coefficient to determine a rifle's 'wind number' is not for me. Neither is a modified/tweaked/scaled version of the G1 method. But if that's what you're into, rock on (being serious). Most shooters have seen this, but the projectile pictured below is what the G1 model was based on:

View attachment 148579

That obviously does not look like any bullet that we shoot out of long range rifles, and the discrepancy is why I would prefer not to use a scaled version of that G1 projectile for much of anything that is considered 'long range'. Why would we move towards G7 models and then custom models for elevation (which is considered the easy part), and then default to an obsolete G1 model for wind (which is considered the hard part)?

yes you are speaking something i brought up years ago and you are completely correct. Here are some considerations:
This is something that in the sniper world is good enough which means it'll get you a enemy stoping kill on a 40" tgt.
G1 can be multiplied in to a G7
BCs change as velocity changes
G1 is a fine starting point for even our G7 ammo up until about 200m before transonic
A ballistic calculator takes all things in to consideration

So if G1 can be consistently multiplied x.512 in to a G7 for us snipers mostly using 308-338 and still have great accuracy why would a G1 not work? G1 and G7 are not same but they are close until trans. If it makes you happy you can do the same formula and just start as G7/.512 = your "bullets perfect wind" and you will crush it

 

[Tangent]

Yes but

yes you are speaking something i brought up years ago and you are completely correct. Here are some considerations:
This is something that in the sniper world is good enough which means it'll get you a enemy stoping kill on a 40" tgt.
G1 can be multiplied in to a G7
BCs change as velocity changes
G1 is a fine starting point for even our G7 ammo up until about 200m before transonic
A ballistic calculator takes all things in to consideration

So if G1 can be consistently multiplied x.512 in to a G7 for us snipers mostly using 308-338 and still have great accuracy why would a G1 not work? G1 and G7 are not same but they are close until trans. If it makes you happy you can do the same formula and just start as G7/.512 = your "bullets perfect wind" and you will crush it

This is why it matters:

A G7 model is not simply a scaled version of a G1 model. And neither model accurately describes our projectile's trajectories.

I get where guys are coming from when they say "it's good enough". I also recognize that when you're shooting larger targets at relatively closer ranges, then G1/G7 differences are negligible (as depicted above by the image from AB).

Although not actually ELR, I shoot out to 1,400 yards about once a week, and that distance is transonic for more than one of my rifles. A scaled G1 model simply results in significant errors relative to the projectiles coefficient of drag at those lower mach numbers. A G7 model fits a little better for a little further, and a customized model (specific to my rifle/ammo) can result in a more accurate coefficient of drag, which results in a more accurate time of flight, which leads to a better model for wind deflection.

Since we are training our brains to evaluate wind conditions, I see no reason to influence our ability (or inability) to call wind with the errors associated with obsolete models.

 

[Deleted member 110997]

This is why it matters:
View attachment 148595

A G7 model is not simply a scaled version of a G1 model. And neither model accurately describes our projectile's trajectories.

I get where guys are coming from when they say "it's good enough". I also recognize that when you're shooting larger targets at relatively closer ranges, then G1/G7 differences are negligible (as depicted above by the image from AB).

Although not actually ELR, I shoot out to 1,400 yards about once a week, and that distance is transonic for more than one of my rifles. A scaled G1 model simply results in significant errors relative to the projectiles coefficient of drag at those lower mach numbers. A G7 model fits a little better for a little further, and a customized model (specific to my rifle/ammo) can result in a more accurate coefficient of drag, which results in a more accurate time of flight, which leads to a better model for wind deflection.

Since we are training our brains to evaluate wind conditions, I see no reason to influence our ability (or inability) to call wind with the errors associated with obsolete models.

Totally correct on training brains for wind.
Since the first ballistic calculator i touched in maybe 2004 there have been options for custom truing, where we set out a pice of AR500 that is 40" wide and 10" tall and true at about 200m pre transonic and as far in to sub as we want. The more data the more accurate and this is what i was taught by Todd many many years ago. With the drag model now trued the computer will then be right for your rifle, with that ammo even if the base was G1 until the 200m before trans.

Thought we were discussing formulas which to Me means doing it in my head and with out a ballistic computer i only have historical dope because I've never bothered to work wind in my head past transonic as wind and drop become a too broad to think through the math problem. I then would be better with a automatic .50 cal.....actually lets be real, id crush anything I've done as a sniper with the M2 .5 cal..... just getting it there and the ammo would be an issue, not to include the drawback of spray and pray collateral.