Range Report Effects of wind on elevation. Aerodynamic jump/drag

[rybe390]

Can we talk about wind for a second? Not in terms of effect on windage, but effects on elevation. Specifically would like to hear thoughts on the effects of headwind on a bullet(and conversely tailwind) and the effects of aerodynamic jump(and if the opposite exists?)

What’s prompting this? This past weekend I shot my .223 AR out to 1,040 yards in Colorado. Wind was 16-46 MPH, hovering at 22-23 mph, and wind was 9-1 o clock. It was my first day shooting in high wind conditions. We made hits successfully and repeatable, but I noticed something when I got home to review everything.

It appeared that the amount of wind was effecting the vertical path of the bullet. I have numbers below to discuss so we have something tangible, but I want to run this past you to make sure I’m adjusting correctly in the future, to create a rule for a rifle/find patterns. I have heard Todd Hodnett call rifles “10mph guns”, when talking about aerodynamic jump, so I’m hoping to understand that better. The below is examples/my thoughts on what’s going on, would like to confirm and pick brains please!

DA of 5850, using 75gr BTHP, AB on Iphone.

Effects of headwind/opposite of aerodynamic jump?
Drop at 1,040 yards in Mils then inches
No wind: 12.9 mils. 483 inches
12 o clock wind, 22.5 mph: 13.2. 494 inches
11 o clock wind, 22.5 mph: 13.3(conditions for the day, making hits) 498 inches
10 o clock wind, 22.5 mph: 13.3. 498 inches
9 o clock wind, 22.5 mph: 13.2. 494 inches

The interesting thing here is the 9 o clock wind. Exact opposite jump of the 3 o clock wind, but in drag.

To me, this looks like the exact opposite of aerodynamic jump, it looks like drag. Every 7 mph is .1 mil of drag if it’s coming from the left, and every 7mph is .1 mil of jump if coming from the right. And, less drag/jump at ¾ ½ value winds.

Effects of aerodynamic jump/how many MPH is .1 mil
No wind: 12.9 mils. 483 inches
3 o clock wind, 22.5 mph: 12.6. 471 inches
2 o clock wind, 22.5 mph: 12.8. 478 inches
1 o clock wind, 22.5 mph: 13. 486 inches

To me, it looks like I have a 7mph gun, meaning full value wind at 3 o clock, every 7mph of wind is .1 mil. 22mph, .3 mil jump. I believe you are able to apply aerodynamic jump to the “value” system for wind as well, shown by the numbers. 2 o clock was less than the 3 value, more than the 1 value. 1 o clock is basically null, and drag from wind comes into play.

Would it make sense to add aero jump to part of a wind call? Dial elevation, make wind call, make calculation for aero jump/aero drag and dial that in, then hold wind?

 

[LastShot300]

The effect of a headwind/tailwind on Aero Jump is negligible. Care only about a crosswind, numbers don't lie.

 

[Lowlight]

You have to note the terrain between you and the target too.

AB Aero Jump has been proven to be overcompensating, we posted the document showing this, so your software is not doing it correctly.

What you are seeing is subsonic/transonic flight which is much more unpredictable and, it's either at bad elevation prediction because you are beyond transonic or you are seeing wind being acting on by the terrain giving rise to the bullet.

Putting a dead set scientific reason on and saying the Apps is accounting for this is really hard to square. I shoot in CO and we have an advantage with less air density, most of the software out there does not manage that well. Especially with the wind, it's always off. Also note, a 3DOF piece of software cannot calculate this stuff, you need 4DOF and 6DOF to do it. Instead, they use flat rate values that technically should not hurt you, but can potentially help fill the gap. But it's only right 50% of the time. Wind is almost never right without truing it like you do elevation.

Shooting to 4000 yards this past weekend, software gave me between 426MOA and 380MOA of adjustment. The actual used was 353MOA, way the hell off. Guys using a kestrel were given 5.7 Mil of wind when we were using about 1.2 Mils but heck that changed every shot. I technically rezeroed the scope for the target, and at subsonic ranges even holding center for 5 shots you have five wildly different impacts.

Putting it in more practical terms, closer to what you were doing. We then shot at 2600 yards. Transonic was 1850 yards. The average hit was 2 on target by some accomplished shooters. Ray and I managed 4 on the last relay. Vertical spread was crazy, I had to fix my position because the average spread was 1.5 MIls plus or minus, but switching up my position I reduced it to .5 Mils. That is a ton of vertical spread. Your ammo is usually a weak vertical link at these distances.

Finally, Max Ord Wind, at 4000 yards Max Ord is 1325ft, at 2600 it was like 425ft, you have no idea what the wind is doing that high in the air. With your 556 your still up there quite a bit. I would have to run it but let's say it's 40ft, that is still 3.5 wind gradients up. So you have to compensate for the wind up in the air.

The software is not all knowing, and there are actually quite a bit of holes in there. Especially 3DOF, vs 4DOF.

As the ground heats, there is also an element of rise in there too. the software does not see this ...

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[Lowlight]

One quick note too,

You are trying to resolve 3.75" at 1040 yards with a 223, that is a tall order.

The shooter is one of the biggest variables, a minor difference in hold can easily move the bullet that much.

The wind alone can definitely exceed that from shot to shot, even if we don't see it clearly. On top of the variation in your load.

Speed is the biggest fix for these problems, if your load is not going fast enough you introduce all sorts of variables.

 

[LastShot300]

Great lesson! thanks Frank.

 

[rybe390]

Frank, thanks for the great explanation here.

Sounds like for my purposes, I have no need to worry about head wind drag, but should take into account jump/fall for longer shots, even though AB over corrects for it?

Obviously, position, spread of ammo, wind call, all play a more important piece here, but, just curious how important calling the jump is once you know how the rifle reacts to crosswind.

In your experience, how much jump have you observed, if any, and am I spinning my wheels here on something that doesn't matter? And, am I correct in saying that with a 3 o clock wind, there is jump, and a 9 o clock wind, there is some form of drag/fall?

 

[Lowlight]

Ignore AJ

It appears at 100 yards, you zero your rifle, you are not gonna see it appear on the target because you already zeroed it out. If you zeroed the rifle at 6 MPH you removed that much from AJ, if you shoot in an 8 MPH wind, you really only have 2 MPH of AJ you might have missed. Even then the target size will absorb the small changes you might see.

this stuff is just telling you what your dope is made of, in other words, it's an ingredient that is included in the mix. The idea you need to account for this externally is completely overblown.

If you dope the rifle first, record your data, and then input the information into your ballistic calculator, you already included every element into the shot. People keep trying to take valid data and add to it because they read this crap that AJ, SD, CE, are all necessary. Sure if you diagram the shot and break down the number into its complete form. But it's not, "you need X MOA to hit your target PLUS all this other data. Once you shoot the target, record the data, you already solved that problem.

Going beyond transonic with any bullet adds an element of unpredictability in the solution because the bullet has slowed down to a point where the effects are all over the place. Your vertical spread is out there, your wind calls, etc. This software can barely handle wind by itself and here we think it can manage all these other issues perfectly. Turn them off, and drive on.

I never turn any of this crap on. I dope the rifle minus software, record the conditions, I head home and then input the details into my ballistic solver and make it match what I shot. I never let the computer tell me what it wants, I tell it what needs to know so it equals my drops. That is how this works, the rifle system cannot match a computer, the computer has to what the rifle system did on the range under the given conditions.

 

[damoncali]

Unless you're making huge wind call changes (say, your dope is at zero wind and the current wind is 30 mph), you're not going to see it and can safely ignore it. And if you are, you're in all likelihood going to miss and get some new dope. (With some exceptions - like short range/rimfire benchrest, where AJ is important simply due to the short range and tiny groups). There are some great F Class shooters that probably don't even know what AJ is and it doesn't hold them back, and they're aiming at a 1/2 MOA x ring.

It's important to understand that AJ is a change int he direction of the shot, and so its dispersion is proportional to range. 1/4 MOA of jump is 1/4 MOA of jump, whether it's at 50 yards or 2000. Wind deflection, however, is NOT proportional to range and gets dramatically worse down range. So the ratio of AJ to wind is much greater at SHORT range, which is why only short range benchrest shooters really care about it. The farther you are shooting, the less you care about AJ - it's a small effect that just gets smaller.

But yes, the jump is down when the wind is to the right if you're shooting a right hand twist. "Jump" refers to the abrupt change in the bullet's departure angle, not the direction of the bullet's movement. If you shoot while skydiving, you'll get a sideways "jump". AJ turns out to be a very important factor if you want to design a targeting system for a fighter plane whose movement relative to the airflow can be highly variable. For ground based small arms, not so much.

 

[rybe390]

Frank, thank you for the great explanation there. Really like the breakdown you included of how these variables all make up your dope/solution but they are not the solution itself. I will for sure be truing my data and compare to untrued and roll from there. I’ll be ignoring AJ from here out, and if it is present, I’ll just dial it out at 100 and keep rolling. I’ll dial SD if I’m far enough for it to actualy matter.

Last question for you, this thread has been super helpful for me so thanks for the time and attention to it. Regarding a headwind/12 o clock wind. Say it’s a 10mph wind, 12 o clock, shooting 800 yards. Would you take this into account for your dope/drop or does headwind not have an effect? I’m going to refer to the calculators again, they seem to think it’s importat. I don’t have enough trigger time to know, hoping you might shed some light on it.

Damoncali, thanks for the proportion example, really put it into frame for me.

 

[Lowlight]

I don't adjust for a head or tailwind - in terms of elevation.

That is often range dependent, guys will see it on "Their Range" which is usually a terrain issue, however, in 90% of the situations, it's a non-issue. Most targets can absorb any small elevation issues that wind might create. It's not the same as saying "You need 1.5 Mils of wind at 800 so you need that same fix for the elevation change with a head or tail wind. It's fractions of an Inch vs a multiple of the plate size as we see with the lateral wind corrections.

Now, never say never, where ever you shoot you have to test it out. At the ranges here in CO that I have shot, it's not uncommon for a head or tail wind and it's never that big an issue, even in the 12MPH to 18MPH winds I see on a weekly basis. I had a bit of a switching wind with the new Revic scope, wind doesn't adjust for wind, that remains a manual fix by the shooter. I tested it out again and it was dead on. So it did not see it.

Now if the bullet is going transonic at 800 yards like with a 223, all bets are off as to what a head or tail will do. The bullet now becomes much less predictable. A prime example of this, several years ago I was hanging out with Clint Smith in Oregon at Thunder Ranch. Doesn't matter the weather Clint stand out in and shoots. We had snow, cold, and were shooting at 1200 yards across a valley. On the opposite side, we had a target up on a hillside. It was snowing and blowing super strong and when Clint shot his 20" 308 with 168s we watch the bullet and the snow blow UP and hit 20ft beyond the target. We could see the effects of the wind pushing the bullet up because the snow was going with it. That was a Wind + Terrain issue, combined with a subsonic bullet.

 

[Nik H]

Ignore AJ

I never turn any of this crap on. I dope the rifle minus software, record the conditions, I head home and then input the details into my ballistic solver and make it match what I shot. I never let the computer tell me what it wants, I tell it what needs to know so it equals my drops. That is how this works, the rifle system cannot match a computer, the computer has to what the rifle system did on the range under the given conditions.

Frank,

When adjusting parameters to get the solver output to match true DOPE, what do you adjust? I use Coldbore so there are lots of knobs to turn and sometimes I veer off into the weeds. I generally only adjust MV when the bullet is supersonic. Is that correct? When is it appropriate to adjust BC versus MV? Is it when you are n the transonic region? What about the elusive Drag Coefficient value in CB? I have never really played with that at all.

Thanks for any insight

 

[LastShot300]

Frank,

When adjusting parameters to get the solver output to match true DOPE, what do you adjust? I use Coldbore so there are lots of knobs to turn and sometimes I veer off into the weeds. I generally only adjust MV when the bullet is supersonic. Is that correct? When is it appropriate to adjust BC versus MV? Is it when you are n the transonic region? What about the elusive Drag Coefficient value in CB? I have never really played with that at all.

Thanks for any insight

I ain't Frank but in my experience with Coldbore, I've never had to fiddle with MV, provided I shot a lengthy string over my Magneto to collect my stats. Trust your chrono (if properly set up) make sure it's not getting wrong data and try to to use the tools in CB to find the velocity stats. I shot transonic and beyond and never had a single issue due to MV. Don't tweak MV as long as you have done your homework. A guy posted time ago, that the DC should be left at its default as long as the BC is correct.

The on/off switches are up to you and they are not different than the ones on FFS, AB, etc. Most people turn them On for no good reason. Just make sure you really get what inputs those switches take in and if you are not 100% confident about the parameters left the switch Off. Best piece of advice I got from Gus.

 

[tna9001]

Frank, could you post this document please?

““AB Aero Jump has been proven to be overcompensating, we posted the document showing this, so your software is not doing it correctly.””

 

[Nik H]

I ain't Frank but in my experience with Coldbore, I've never had to fiddle with MV, provided I shot a lengthy string over my Magneto to collect my stats. Trust your chrono (if properly set up) make sure it's not getting wrong data and try to to use the tools in CB to find the velocity stats. I shot transonic and beyond and never had a single issue due to MV. Don't tweak MV as long as you have done your homework. A guy posted time ago, that the DC should be left at its default as long as the BC is correct.

The on/off switches are up to you and they are not different than the ones on FFS, AB, etc. Most people turn them On for no good reason. Just make sure you really get what inputs those switches take in and if you are not 100% confident about the parameters left the switch Off. Best piece of advice I got from Gus.

Thanks LS!

I always leave the switches off as I seldom have the opportunity to shoot beyond 600 yards. The nearest 1,000 yard range is 3 hours away. However, I find that even at 600 yards, the results are a tiny bit off. I don't have a chronometer as I shoot factory only. I borrow a friends chrono and measure the MV of all the cartridges I use. He has an old school one which is placed about 13 feet away. CB does use a retardation factor that I have used. As I said, the difference is slight. It amounts to about 0.1 mil at 500 and 600 yards.

In all honesty, I use CB to get me in the zone and then record the true DOPE in a data book which is always with me. That is the bible.