No value winds and how they affect bullets

[Eurodriver]

Common sense says with a no value wind (we will assume for purposes of this thread by no value I mean winds coming AT the shooter at 12:00) you will increase drag on the bullet, slowing it and causing it to drop slower.

That's what I was always trained to compensate for, am I not correct?

Are there any other variables present on a bullet flying into tough no value winds? Will it cause loss of stability increasing MOA? (unrelated to the round going transonic earlier)

Are there charts or anything to compensate for no value winds?

Editted because I am an idiot.

[Deputy Dan]

Brother, winds from 3 o'clock or 9 o'clock are full value.

Winds from 12 o'clock or 6 o'clock are no value winds.

[a0cake]

Winds from the 6 and the 12 are commonly called no value winds, not full value.

While head and tail winds are said to have no value, in reality they do have a minor effect.

Conventional wisdom says shooting into a headwind lowers POI. Shooting with a tailwind raises it.

It's a function of time of flight more than anything else. Remember, two identical objects will fall at the same rate regardless of velocity. A loose bullet simply dropped by hand will hit the ground at the exact same time as a bullet fired at 3,000 FPS on a level plane from the same height.

Since a headwind increases TOF your POI will go down because gravity will have more time to "pull the bullet down."

How much? A 77 GR SMK out of a MK12, for example, will need ~ 0.3 more MILS of UP elevation adjustment at 1000m with a 20 MPH headwind. (I'm using extreme numbers to illustrate that while there IS a difference, it is very slight.) Use a realistic range and 10MPH wind and you'll find that you don't need to worry about it much.

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^^^ That's conventional wisdom.

I have my own thoughts. Here they are:

This diagram is something I've come up with that IMO is a bit more accurate in certain circumstances.

When you have a Zero where the trajectory of the round crosses above LOS, an increase in the bullet's TOF on the way to the target (but on the near side of the no wind apogee...which also coincides with maximum ordinate of the trajectory), can actually require HOLDUNDER.

Why? Because until the round hits max-ord, the round is still moving up relative to LOS. Therefore, increasing TOF to a short range target (any range before max-ord) can and does make for a higher, not lower POI. Once the round hits the highest point of the trajectory, revert back to the conventional answer I outlined above and expect to see a lower POI.





All of this is pretty academic though. Unless you're a competition BR shooter none of it matters much IMO. I don't believe headwind or tailwind will sufficiently raise or lower POI to any quantifiable or significant level in a tactical environment.


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Also, here is a better set of rules than thinking using the traditional wind values method, which is actually pretty wrong.

MPH X C = adjusted MPH

If wind direction is 90 degrees from sightline C = 1.0
If wind direction is 65 degrees from sightline C = .9
If wind direction is 45 degrees from sightline C = .75
If wind direction is 30 degrees from sightline C = .5
If wind direction is 15 degrees from sightline C = .25
If wind direction is 0 degrees from sightline C = 0

[Eurodriver]

Wow, I'm not sure how I screwed that up. Thanks DD and a0.

Winds from the 6 and the 12 are commonly called no value winds, not full value.

While head and tail winds are said to have no value, in reality they do have a minor effect.

Conventional wisdom says shooting into a headwind lowers POI. Shooting with a tailwind raises it.

It's a function of time of flight more than anything else. Remember, two identical objects will fall at the same rate regardless of velocity. A loose bullet simply dropped by hand will hit the ground at the exact same time as a bullet fired at 3,000 FPS on a level plane from the same height.

Since a headwind increases TOF your POI will go down because gravity will have more time to "pull the bullet down."

How much? A 77 GR SMK out of a MK12, for example, will need ~ 0.3 more MILS of UP elevation adjustment at 1000m with a 20 MPH headwind. (I'm using extreme numbers to illustrate that while there IS a difference, it is very slight.) Use a realistic range and 10MPH wind and you'll find that you don't need to worry about it much.

------------------------------------------------------------------------

^^^ That's conventional wisdom.

I have my own thoughts. Here they are:

This diagram is something I've come up with that IMO is a bit more accurate in certain circumstances.

When you have a Zero where the trajectory of the round crosses above LOS, an increase in the bullet's TOF on the way to the target (but on the near side of the no wind apogee...which also coincides with maximum ordinate of the trajectory), can actually require HOLDUNDER.

Why? Because until the round hits max-ord, the round is still moving up relative to LOS. Therefore, increasing TOF to a short range target (any range before max-ord) can and does make for a higher, not lower POI. Once the round hits the highest point of the trajectory, revert back to the conventional answer I outlined above and expect to see a lower POI.





All of this is pretty academic though. Unless you're a competition BR shooter none of it matters much IMO. I don't believe headwind or tailwind will sufficiently raise or lower POI to any quantifiable or significant level in a tactical environment.


--------------------------------------------------------------------------------------------------------------------------------------------------------------

Also, here is a better set of rules than thinking using the traditional wind values method, which is actually pretty wrong.

MPH X C = adjusted MPH

If wind direction is 90 degrees from sightline C = 1.0
If wind direction is 65 degrees from sightline C = .9
If wind direction is 45 degrees from sightline C = .75
If wind direction is 30 degrees from sightline C = .5
If wind direction is 15 degrees from sightline C = .25
If wind direction is 0 degrees from sightline C = 0

The bolded is what I was most concerned about. I was shooting out to about 600 yards yesterday in no value winds coming directly at me. I was concerned that in no winds or winds coming from the 6:00 I would be facing a situation where my POI would be higher...but I am not a competition bench rest shooter and an inch, or even a few inches of increased elevation is not an issue at all.

Thanks for the information.

[Deputy Dan]

a0cake gave you excellent info.

I shoot 6mmBR at Shippensburg PA, and winds there are a bitch most of the time. Clinch River 106gr VLDs help at 600+.

[kartoffel]

Great diagram.

My only suggestion is to consider not the apogee of the trajectory, but the point where the trajectory is parallel to the inclination of the wind. Wind doesn't always blow horizontally, e.g. say you're shooting uphill into a headwind coming down the mountain.

[steve--oh]

The B4 next to me says no compensating for no value, blowing in either direction.

And he's a stone cold killer.

[a0cake]

The B4 next to me says no compensating for no value, blowing in either direction.

And he's a stone cold killer.

Yep, and for all intents and purposes he's right. But sometimes it's worth it to dive into minutia, if for no other reason than to understand "why."

[Sgt_Gold]

You would need a hell of a head wind to affect the trajectory of a rifle round. If you're shooting into that fast of a headwind you better be staked down.

[QuietShootr]

Winds from the 6 and the 12 are commonly called no value winds, not full value.

While head and tail winds are said to have no value, in reality they do have a minor effect.

Conventional wisdom says shooting into a headwind lowers POI. Shooting with a tailwind raises it.

It's a function of time of flight more than anything else. Remember, two identical objects will fall at the same rate regardless of velocity. A loose bullet simply dropped by hand will hit the ground at the exact same time as a bullet fired at 3,000 FPS on a level plane from the same height.

Since a headwind increases TOF your POI will go down because gravity will have more time to "pull the bullet down."

How much? A 77 GR SMK out of a MK12, for example, will need ~ 0.3 more MILS of UP elevation adjustment at 1000m with a 20 MPH headwind. (I'm using extreme numbers to illustrate that while there IS a difference, it is very slight.) Use a realistic range and 10MPH wind and you'll find that you don't need to worry about it much.

------------------------------------------------------------------------

^^^ That's conventional wisdom.

I have my own thoughts. Here they are:

This diagram is something I've come up with that IMO is a bit more accurate in certain circumstances.

When you have a Zero where the trajectory of the round crosses above LOS, an increase in the bullet's TOF on the way to the target (but on the near side of the no wind apogee...which also coincides with maximum ordinate of the trajectory), can actually require HOLDUNDER.

Why? Because until the round hits max-ord, the round is still moving up relative to LOS. Therefore, increasing TOF to a short range target (any range before max-ord) can and does make for a higher, not lower POI. Once the round hits the highest point of the trajectory, revert back to the conventional answer I outlined above and expect to see a lower POI.





All of this is pretty academic though. Unless you're a competition BR shooter none of it matters much IMO. I don't believe headwind or tailwind will sufficiently raise or lower POI to any quantifiable or significant level in a tactical environment.


--------------------------------------------------------------------------------------------------------------------------------------------------------------

Also, here is a better set of rules than thinking using the traditional wind values method, which is actually pretty wrong.

MPH X C = adjusted MPH

If wind direction is 90 degrees from sightline C = 1.0
If wind direction is 65 degrees from sightline C = .9
If wind direction is 45 degrees from sightline C = .75
If wind direction is 30 degrees from sightline C = .5
If wind direction is 15 degrees from sightline C = .25
If wind direction is 0 degrees from sightline C = 0

Brilliant. Possibly too detailed to matter in the real world, but elegant nonetheless. Thanks.