Care should be taken when using angle compensated distances from your LRF

[Glassaholic]

I posted this in another thread on rangefinders, but thought I should post this as it's own thread. While most manufacturers offer some kind of angle compensated distance mode for their rangefinder, you should use that mode with caution because the one thing the rangefinder cannot compensate for is wind and if you use the compensated value which will be shorter than the line of sight (LOS) value and you punch that into your ballistics calculator you could end up with an incorrect wind hold value. I put this below chart together because I am a visual learner and thought this might help better explain why the wind value is different between the two measurements.

EDIT: @TacticalDillhole has pointed out this is NOT an issue if you have an LRF with Bluetooth that is connecting to the Kestrel and providing the solution for both drop AND wind, which is something to keep in mind. This is ONLY for LRF units that are stand alone, or LRF units that have built in ballistics (for drop) but no connectivity to identify wind holds.

It has also been pointed out that rarely will we shoot at such extreme angles, even when hunting in the mountains, so if we reduce the angle in the above example from 40° to 15° then the variance for the wind is even less, and one could argue whether the ability to guesstimate wind at distance (especially in mountain terrain with hills, valleys, cliff faces, etc.) is of greater concern than the error introduced by the angle adjusted distance. The below chart maps out what this difference could mean:

 

[pbatesaz]

Tag

 

[Crazy1323]

I think you might be missing something.

The amount of wind drift has nothing to do with the distance traveled or velocity of the bullet (but these can be components of the calculation). The wind drift is affected by the amount of time that the bullet is exposed to the wind. In your example, the travel of the bullet in the X axis is 385 yards, however since the Bullet is traveling up some, the distance that the bullet travels through the air is greater than 385 yards. By traveling a longer distance it is exposed to the wind for a longer duration of time, and therefore drifts more. Also, since you are firing at an upward angle, the velocity of the bullet is slowing more rapidly than if it were fired flat. While the horizontal velocity isnt affected by this, the bullet will be in the air for a longer duration of time, thus causing more wind shift.

So..... Is the wind shift in your proposed shot .72? No, it is some value greater than that. The example you gave above may factor these items in where the .98 value is correct but I do not know without know what formulas they are using and I dont want to do the calls at the moment.

The metric that matters for wind drift is time of flight, not really velocity of the projective or distance it travels (But you can compute time of flight using distance and velocity).

I hope this helps.

 

[Crazy1323]

EDIT: I think I might have misread your original post. You are saying that the RF would return you a reading of 385 yards even though the object is 500 yards away. I thought you were saying that the RF gave you a reading greater than the distance to the object when compensating for angle.

 

[Glassaholic]

EDIT: I think I might have misread your original post. You are saying that the RF would return you a reading of 385 yards even though the object is 500 yards away. I thought you were saying that the RF gave you a reading greater than the distance to the object when compensating for angle.

That is correct, but you are correct in that the longer distance and wind deflection is based on time of flight, ballistic coefficient, etc. and how much all that is affected by wind over a given distance and period of time. My example uses a 308 with 175 grain projectile, but plug in numbers for the same 175 grain projectile but from a 300 Win Mag moving say 300fps faster and you'll notice the difference between the 500 yards LOS and 385 yards angle adjusted is less; however, there will still be a difference because the wind still has the opportunity to affect the flight of the bullet for 115 yards further even though time of flight may be shorter. Ultimately, the value that needs to be plugged into the ballistic calculator is the LOS distance with the angle inputted as well and not the angle adjusted distance that is provided by many LRF's.

 

[_Windrider_]

Why can’t you use the angle compensated distance? All it takes is a simple understanding of trig and a simple mathematical calculation to get the horizontal distance to the target. Most LRF’s tell you the angle as well.

As with anything you just have to understand what you are doing.

 

[Glassaholic]

Why can’t you use the angle compensated distance? All it takes is a simple understanding of trig and a simple mathematical calculation to get the horizontal distance to the target. Most LRF’s tell you the angle as well.

As with anything you just have to understand what you are doing.

Read my first post, I explain why you should not use the angle compensated distance for inputting into your ballistics calculator, I then provide a graph that also explains this???

 

[_Windrider_]

But don’t most LRF’s connect directly to your BC and do all this for you? I mean the three I have connect via Bluetooth and do it all. I guess maybe you could clarify to not manually input the compensated distance in the distance to target field. Instead use horizontal distance and input the look angle?

 

[seansmd]

But don’t most LRF’s connect directly to your BC and do all this for you? I mean the three I have connect via Bluetooth and do it all. I guess maybe you could clarify to not manually input the compensated distance in the distance to target field. Instead use horizontal distance and input the look angle?

Mine (leica2800.com) sends the los distance, dof, and angle and the kestrel died the proper math. Many lrf don't send the angle or dof.

 

[_Windrider_]

Mine sends the distance, dof, and angle and the kestrel died the proper math. Many lrf don't send the angle or dof.

DOF is meh. I don’t subscribe to big Coriolis or SD stuff.

But the reason the BC asks for the angle is it assumes you are inputting the distance read from the LRF which is line of sight. That’s how it gives you your elevation number. Then it does the trig and gives you the wind number.

The key is you have to input the angle as well, if you don’t then the original post is accurate. You will mis.

 

[seansmd]

DOF is meh. I don’t subscribe to big Coriolis or SD stuff.

But the reason the BC asks for the angle is it assumes you are inputting the distance read from the LRF which is line of sight. That’s how it gives you your elevation number. Then it does the trig and gives you the wind number.

The key is you have to input the angle as well, if you don’t then the original post is accurate. You will mis.

That was the premise of OP the wind being wrong.

Edit- I miss read yours, you are coming at it if you use los and don't enter angle you miss vertically, he was saying if you use amr you can miss wind.

 

[Glassaholic]

But don’t most LRF’s connect directly to your BC and do all this for you? I mean the three I have connect via Bluetooth and do it all. I guess maybe you could clarify to not manually input the compensated distance in the distance to target field. Instead use horizontal distance and input the look angle?

Ah yes, that's an excellent point Tac, but I would not say that "most" LRF's connect with ballistic calculators, I would say most do NOT connect with ballistic calculators, and those that do or have a built in ballistic calculation do not connect to a Kestrel to provide wind values in the solution so even if you get the proper drop value your wind will still be off - IF you are using the angle adjusted value. Unless you are running a Sig Kilo 2400ABS or a Leica CRF 2800.COM or Sig BDX3000 that is connecting to a Kestrel you're not going to have wind solutions. I'm going to update my original post to indicate this caveat.

 

[Lowlight]

You never want to use corrected values with your ballistic computer

you use the straight line distance and then include the angle of the shot.

The corrected values will never work right

 

[Glassaholic]

That was the premise of OP the wind being wrong.

Edit- I miss read yours, you are coming at it if you use los and don't enter angle you miss vertically, he was saying if you use amr you can miss wind.

That is correct sean, that is what I'm saying, if you are using HCD or AMR or whatever your manufacturer is calling their angle adjusted/corrected distance, and you use that distance to plug into your ballistics calculator, your wind is going to be wrong. Instead, you should be using the LOS distance and ALSO inputting the angle in order to get correct drop AND wind values from your ballistics calculator.

 

[dgheriani]

Although what you've put forward here (use LOS distance+angle instead of AMR distance) is correct, it isn't as much of a difference as your example illustrates. A 15 degree angle doesn't turn 500 yards into 385, it turns it into 482 and I'd posit that for the vast majority of calibers, that difference wouldn't change the wind call. It'd have to be a 40 degree angle to turn 500 into 385. It's pretty simple trig, you multiply the cosine of the angle by the distance. The cosine of 15 is roughly 0.96. The difference is important for the elevation component but not really for the wind call until you get higher than 20-25 degrees. I don't know where Hornady (or whoever) got the numbers in that chart but that isn't right.

 

[TheGerman]

We should really change the thread title to 'Remember to use more wind on cosine calculated distances'

 

[Sheldon N]

As if any of us encountered such a shooting situation AND could call the wind accurately enough that the 0.1 mil of difference in angle compensated wind hold was the deciding factor.

What I can tell you from experience is that there is a LOT more wind trickery including vertical displacement when dealing with significant terrain, cliff faces and wind. Strong winds aloft making turbulent "eddy" currents in front of cliff faces as they rush over, winds rushing up hill faces lifting the bullet, cross winds adding both horizontal and vertical as the wind picks up and dies off. If you are in that kind of terrain where you are making a high angle shot you have a lot more to think about than just your AMR.

 

[dgheriani]

As if any of us encountered such a shooting situation AND could call the wind accurately enough that the 0.1 mil of difference in angle compensated wind hold was the deciding factor.

What I can tell you from experience is that there is a LOT more wind trickery including vertical displacement when dealing with significant terrain, cliff faces and wind. Strong winds aloft making turbulent "eddy" currents in front of cliff faces as they rush over, winds rushing up hill faces lifting the bullet, cross winds adding both horizontal and vertical as the wind picks up and dies off. If you are in that kind of terrain where you are making a high angle shot you have a lot more to think about than just your AMR.

Lies! if you hold the wind your Kestrel says to hold (and don't use AMR wind) you'll hit. It's science

 

[Glassaholic]

Although what you've put forward here (use LOS distance+angle instead of AMR distance) is correct, it isn't as much of a difference as your example illustrates. A 15 degree angle doesn't turn 500 yards into 385, it turns it into 482 and I'd posit that for the vast majority of calibers, that difference wouldn't change the wind call. It'd have to be a 40 degree angle to turn 500 into 385. It's pretty simple trig, you multiply the cosine of the angle by the distance. The cosine of 15 is roughly 0.96. The difference is important for the elevation component but not really for the wind call until you get higher than 20-25 degrees. I don't know where Hornady (or whoever) got the numbers in that chart but that isn't right.

The chart was an "example" and the picture used was from Vortex, they didn't list the angle so I just plugged in an angle at random to "provide an example"; however, I'm glad you brought this up because the angle does not change the wind value, if I plug in the same information into the ballistics calculator but use a 40° angle instead of 15° the wind value is still the same which means the "hold" value is still going to be wrong when using angle adjusted distances from your LRF:

If you don't feel the difference is going to matter that's fine, but the fact still remains that if you use an angle adjusted value from an LRF that is not already connected to a Kestrel or the like that is providing wind feedback, then your wind hold is going to be incorrect. Now, if you feel other wind conditions are going to impact your bullet more than the incorrect ballistics hold that's okay, but I'd rather rule out all possible errors so that my estimate of the wind in those conditions is reduced as much as possible.

 

[dgheriani]

The chart was an "example" and the picture used was from Vortex, they didn't list the angle so I just plugged in an angle at random to "provide an example"; however, I'm glad you brought this up because the angle does not change the wind value, if I plug in the same information into the ballistics calculator but use a 40° angle instead of 15° the wind value is still the same which means the "hold" value is still going to be wrong when using angle adjusted distances from your LRF:
View attachment 7132271

If you don't feel the difference is going to matter that's fine, but the fact still remains that if you use an angle adjusted value from an LRF that is not already connected to a Kestrel or the like that is providing wind feedback, then your wind hold is going to be incorrect. Now, if you feel other wind conditions are going to impact your bullet more than the incorrect ballistics hold that's okay, but I'd rather rule out all possible errors so that my estimate of the wind in those conditions is reduced as much as possible.

This is one of those things people make a big deal about when they look at the numbers of it but in practice it doesn't equate to much. Sure, the windage call will be off if you use AMR distance for a 40 degree shot but have you actually ever shot at anything at a 40 degree angle? It's quite severe. If you're ever shooting at something at that steep an angle, for sure, you need to keep in mind to use the wind call from the LOS range. It's just not something that happens often, in regular applications. I live in the mountains and shoot high angle stuff multiple times a week and a 25 degree shot is steep. Also, like Sheldon pointed out, once you're shooting in mountainous terrain, the wind is doing all kinds of funky things as it contours the slopes. For shots 20 degrees and less, the difference in the wind call is less than most mortal men's ability to call the wind anyways (even assuming constant wind). It's one of those things that if you have all the time in the world, sure, plug in LOS range and the angle. It's just much more expedient to use the AMR range and go from there, especially if under any kinda time constraint.

 

[Glassaholic]

It's just much more expedient to use the AMR range and go from there, especially if under any kinda time constraint.

But why, why use AMR at all? Why not just set your non-connected LRF to LOS distance?

 

[_Windrider_]

But why, why use AMR at all? Why not just set your non-connected LRF to LOS distance?

Just like connecting to your BC, not all of them have inclinometers. Many just give you a distance of what they are pointing at b

 

[NoLegs24]

I'm going to be belligerent and use the Inclination Range from the Vectors like I always do, and see how that plays out next week at Hat Creek Training. haha. Steep as F* over there...

But yes, Bryan Morgan at HCT has mentioned about not using the Inclination Range on his Vector21's for that exact reason. But, he's also one of those guys who actually needs to take that into account cause of where he shoots.

I get it. I just don't like to listen

 

[nfoley]

This is an interesting discussion I have not thought about. I always use angle compensated distances from my Fury RF Binos. Prior to that I would have a lot of high and low misses from not getting an inaccurate angle using my cell phone (shooter app) to determine angle. Once I started using angle compensated distances I noticed much less difficulty getting correct vertical data.
With wind I seem to always start with a guesstimate, and adjust after figuring out what the wind was on first target. I am wrong so often on the initial guess that maybe for me the incorrect wind hold wouldn't matter much.
Definitely going to play with this next time I'm shooting high angles.

 

[wade2big]

Interesting point but it seems it could be overthought and overblown just like the difference between a 1/2” gun and a 3/4” gun or ammo with a sd of 8 or 16. None of that stuff matters much when the distances stretch since the mechanical error is much smaller than the human error. I agree with @dgheriani.

 

[Glassaholic]

Just like connecting to your BC, not all of them have inclinometers. Many just give you a distance of what they are pointing at b

That's a good point as well, if you don't have an ACI and you don't have an LRF that can feed you the angle then you're just guessing at the angle, if you're even putting one into your Ballistics Calculator (BC). I can see where the rule of diminishing returns might be at play, and each shooter has to choose what they'll fall on their sword over. The good news is that with new connectivity, we're seeing more devices connecting with Kestrel's like the Leica 2800.COM, Sig Kilo 2400ABS and the like, hopefully we'll see even more solutions down the road that communicate and deliver accurate hold values for drop and wind. In fact, there is technology right on the horizon that will be able to detect wind at distance, this will be a game changer more than any of this for sure.

 

[dgheriani]

But why, why use AMR at all? Why not just set your non-connected LRF to LOS distance?

You use AMR because the difference the angle makes to the elevation matters much more than it does to the windage. Your earlier example of a 15 degree angle means that for your 500 yard LOS shot, you need to use the dope for 482 for your elevation which will be different than your elevation dope for 500. You can potentially miss high if the target is small enough. You're also dealing with absolutes here, you know (or should know) that your elevation dope is good and you know what the distance is (thanks to your lrf). Your wind hold will be the same for 482 as it would be for 500 and even if it was off say 0.1 your wind call isn't an absolute. It's based on say the wind you've measured at your position as well as what you see downrange. It's an educated guess. 0.1 of variance is just noise.

All this being said, if you have all the time in the world, sure, punch in LOS distance and angle and then scroll to your correct dope. It's just more data that you have to manually enter for each target, hence it being slower than getting your AMR range and then looking up your dope. It also just doesn't matter all that much until you get into 20+ degree angles.

Like you said, technology is helping us out to not have to worry so much about this these days anyways. I run Sig K3000s linked to my Kestrel and they give me bang on dope for whatever I laze. My point in all this was just that worrying about using LOS range for wind although correct, isn't that big a deal until the angle gets real steep.

 

[seansmd]

You use AMR because the difference the angle makes to the elevation matters much more than it does to the windage. Your earlier example of a 15 degree angle means that for your 500 yard LOS shot, you need to use the dope for 482 for your elevation which will be different than your elevation dope for 500. You can potentially miss high if the target is small enough. You're also dealing with absolutes here, you know (or should know) that your elevation dope is good and you know what the distance is (thanks to your lrf). Your wind hold will be the same for 482 as it would be for 500 and even if it was off say 0.1 your wind call isn't an absolute. It's based on say the wind you've measured at your position as well as what you see downrange. It's an educated guess. 0.1 of variance is just noise.

All this being said, if you have all the time in the world, sure, punch in LOS distance and angle and then scroll to your correct dope. It's just more data that you have to manually enter for each target, hence it being slower than getting your AMR range and then looking up your dope. It also just doesn't matter all that much until you get into 20+ degree angles.

Like you said, technology is helping us out to not have to worry so much about this these days anyways. I run Sig K3000s linked to my Kestrel and they give me bang on dope for whatever I laze. My point in all this was just that worrying about using LOS range for wind although correct, isn't that big a deal until the angle gets real steep.

Others have said AMR calculations are wrong, not sure where this originated or if it is correct.

 

[AbbyKatt]

You never want to use corrected values with your ballistic computer

you use the straight line distance and then include the angle of the shot.

The corrected values will never work right

How much of an angle makes a difference? Does it matter if you are standing to take the LR reading but then take the shot prone? My assumption is that the 5-6' difference would not matter.

 

[dgheriani]

Others have said AMR calculations are wrong, not sure where this originated or if it is correct.

If you're shooting at an angle, it is correct to use the AMR distance for your elevation. You should use LOS distance for your wind hold although in reality, it doesn't make a perceptible difference until you get to 20+ degrees of inclination.

 

[Sheldon N]

Some real world examples of the kind of funky crap that terrain + wind does.... all from the past 2 weeks.

Where I shoot has a combination of level shooting areas plus moderately steep slopes where targets are set. Shooting 223 at 600 yards, target on a hillside face, wind quartering against it. Watched my dope lose 0.4 mils for about ten minutes, then have it come back again. With misses you could see the dust just ripping up the face of the hill.

Shooting at 950 yards two days ago with my Dasher match loads, similar terrain again except a quartering headwind from the left. There was a solid 2 mil left hold, plus the general turbulence of the wind coming over the top of the far hillside and down the face. That turbulence took what is a extremely accurate perfect waterline load and added about 0.3mil of almost random vertical dispersion. To the point where I said "screw this" and stopped shooting at that target entirely. Moved over to a lower valley 800 yard target sheltered from the wind and the gun hammered again at 1 MOA steel.

The kind of angle where you would see the AMR wind issue become a real problem is STEEP, like no joke standing at the top of a black diamond ski run kind of steep. And when you deal with wind interacting with big terrain like that, it's no longer a simple left to right do the angle math problem, it's more wholistic where you look at where is the wind coming from and what is it going to do when it runs over that cliff face or up this valley. And the degree of uncertainty for a first round hit is much, much higher than on flat ground.

 

[Glassaholic]

You use AMR because the difference the angle makes to the elevation matters much more than it does to the windage. Your earlier example of a 15 degree angle means that for your 500 yard LOS shot, you need to use the dope for 482 for your elevation which will be different than your elevation dope for 500. You can potentially miss high if the target is small enough. You're also dealing with absolutes here, you know (or should know) that your elevation dope is good and you know what the distance is (thanks to your lrf). Your wind hold will be the same for 482 as it would be for 500 and even if it was off say 0.1 your wind call isn't an absolute. It's based on say the wind you've measured at your position as well as what you see downrange. It's an educated guess. 0.1 of variance is just noise.

All this being said, if you have all the time in the world, sure, punch in LOS distance and angle and then scroll to your correct dope. It's just more data that you have to manually enter for each target, hence it being slower than getting your AMR range and then looking up your dope. It also just doesn't matter all that much until you get into 20+ degree angles.

Like you said, technology is helping us out to not have to worry so much about this these days anyways. I run Sig K3000s linked to my Kestrel and they give me bang on dope for whatever I laze. My point in all this was just that worrying about using LOS range for wind although correct, isn't that big a deal until the angle gets real steep.

The reason I asked is because to use or not use AMR has the same issue, you are going to introduce error. But then it dawned on me what you're getting at (sometimes I'm slow) and what you're saying is that until you get into some pretty extreme angles, the difference of the elevation drop is going to make more of a difference then possibly the wind hold value. So in essence you are looking at the possible errors from either and have decided that the wind error is the lessor of two evils. That, I can wrap my head around and it makes sense for those who may not have the equipment or the time to adjust appropriately. Maybe I should rename my thread so it doesn't sound so disastrous if you use AMR, HCD, etc. for your distance that you plug into your BC but simply to be aware. Thanks for being patient and explaining where you're coming from.

And I agree, ones ability to call or identify wind at distance makes more of a difference here. If you're off by 1mph in your wind guesstimate then you could be way off by the time you get to 1000 yards or thereabouts.

Long range shooting consists of both science and art. The science part comes in our ballistic calculations but the art comes in knowing your equipment (rifle, cartridge, dope, LRF, etc.) and its limitations, and accurately assessing what the wind is doing between you and the target. Squeezing the trigger is the easy part

 

[Glassaholic]

I have added another chart to the original post which I think helps clarify the drop error. In the end having technology that can account for both drop, angle and wind (among other atmospherics) can really help to eliminate errors; however, if you are using something like a Kestrel to measure wind you must keep in mind this is wind "at the shooter" which does not always represent the wind that will impact the flight of the bullet as it travels above various terrain and conditions on its way to the target.