4DOF inclined fire error

[Bevan]

I get wildly different results for inclined fire with 4DOF vs Applied Ballistics Quantum & other calcs.

The 4DOF app provides a solution with much greater difference between flat and angled fire than all other calculators.

Using inputs of
MV 2747
Bullet: Hornady .22 80gr ELDM (using drag model in 4DOF, and g7 bc of .244 in other apps)
1:8 twist
Sight height 42mm
Zero range 100M
target range 600m
Standard atmosphere at 0m ASL
wind 1m/s from 270 deg
target at 600m, flat or -20 deg angle.
elevation correction in mils
azimuth 114 latitude -043

See this table for the results from 4 different solvers:

Any clever ideas? Has anyone else found this with 4DOF? Real-world results for flat shooting are great for me with 4DOF. However, I've been using AB because the real-world results for angled shots seem to match up better.

 

[JustSendit]

I get wildly different results for inclined fire with 4DOF vs Applied Ballistics Quantum & other calcs.

The 4DOF app provides a solution with much greater difference between flat and angled fire than all other calculators.

Using inputs of
MV 2747
Bullet: Hornady .22 80gr ELDM (using drag model in 4DOF, and g7 bc of .244 in other apps)
1:8 twist
Sight height 42mm
Zero range 100M
target range 600m
Standard atmosphere at 0m ASL
wind 1m/s from 270 deg
target at 600m, flat or -20 deg angle.
elevation correction in mils
azimuth 114 latitude -043

See this table for the results from 4 different solvers:
View attachment 8782333

Any clever ideas? Has anyone else found this with 4DOF? Real-world results for flat shooting are great for me with 4DOF. However, I've been using AB because the real-world results for angled shots seem to match up better.

So i admittedly used 4dof much less than AB. I did see a difference shooting angles as big as 30 degrees. Personally, AB lined out more accurately for me.

 

[Bevan]

I need to go shoot on steel in controlled (non match) conditions and document the results. But really interested in any info on this. I like the 4DOF interface a lot more than AB and I'd like to be able to trust it - I've found it perfect on shots without angle.

@Ledzep any ideas ?

 

[Ledzep]

Let me talk to Jayden tomorrow. I know he was looking into this earlier this year, but I haven't heard if anything was found.

 

[LastShot300]

4DOF is wrong since its debut when it comes to angle fire solutions.

 

[Bevan]

Let me talk to Jayden tomorrow. I know he was looking into this earlier this year, but I haven't heard if anything was found.

Thanks, let me know what he reckons

 

[davsco]

don't most rangefinders give the horizontal effective distance? what am i missing (surely something)?

 

[Bevan]

don't most rangefinders give the horizontal effective distance? what am i missing (surely something)?

Yes, and you can see in my table in the OP what the elevation correction for my scenario is if using a EHD range, vs the angled solution for line of sight range. There is a small difference, because the EHD accounts for the partial gravity vector, but does not account for time of flight. The longer the range or the greater the angle, the greater the error induced by using EHD.

In this case its 0.13MRAD if using AB, or you'd have a dialled error of 0.2 which is significant

 

[davsco]

aha i think i see what you're saying, and it makes sense. the actual distance has to be used as it affects time in the air and thus windage, where the horiz effective distance would be used for drops. so you'd need to input actual distance and angle and the program should calc/know the horiz distance. i was just trying to understand tbe issue... not helpful in answering you though...

 

[Bevan]

For my example ballistic solution, there is a 0.08 second time of flight difference between 600m LOS, or EHD of 600m @ 20 deg which is 563m.

0.93 sec vs 0.85 sec

This means that although the EHD solution accounts for the change in gravity vector on drop, the bullet still experiences greater drag over the longer time of flight, and actual elevation required will be more than the EHD solution provides. There will also be a windage difference.


For shorter ranges, smaller angles, and larger targets EHD is absolutely fine, e.g. for hunting purposes inside 400 metres.

 

[Ledzep]

We're still looking into it. We've got reports from several of our sponsored shooters and I've seen these posts pop up from time to time as well. There have been a couple of matches where half of the attendees let us know they were off by a large margin at a specific target.

We have gone to Cameo and tested this with 5 different rifles/profiles and were unable to find any holes (500ish yd, 20-30 degree incline). Independently, several of us here have gone to various places out west (1200yd @15 degrees I think is the longest/highest) to test this and when we've done that our profiles lined up really close to reality. We're planning a trip to specifically test this feature to the fullest extent with the radar along.

There's still a lot that myself, Joe, and Jayden need/want to look at. We have a 6DoF engine that we're going to run some reference shots and see how the results compare to 4DoF and verify there's nothing silly going on with reference planes or whatever in the app. Another thing to consider is that in the locations where this happens, there is often vertical wind. There is no way to put vertical wind into the calculator, and I don't know a method to determine (from a shooting position) what the input would even be if you could. Every solver I'm aware of treats the wind as though it is perfectly level with gravity. However, in the world, wind follows terrain. This disparity can be worth more than you might initially think and is most notable with head/tail winds. If you set up a shot in 4DoF shooting up-hill, watch what happens when you put a head wind and increase the value. Relative to your line of sight, the wind is blowing the bullet "up" at whatever the incline angle is, because relative to gravity, the wind is horizontal (I can just imagine the mind bending thought I just created...)

A prime example in my memory is the Hornady PRC, the stage where there's a 1 mile target. Throughout the whole match leading up to that target dope for everyone lines up perfect, then you shoot up this draw (wind tunnel) that goes up-hill to the 1 mile target, and what every single person noted was a 0.8-1.4 mil deviation from dope at a mile that worked its way down to being correct by the base of the hill. In this situation it was a tail wind (which would, with level wind push your relative POI down), but the wind was blowing up-hill, and at least to some extent slowing the bullets' descent. Double whammy-- the calculator thinks you should hit low because of angle fire with level tail wind, plus the fact that in reality the wind is actually following terrain and reducing drop.

I'm not saying that's always what's happening, just pointing out that it's sometimes difficult to know that it's happening, or especially to parse it out from solver errors, even if you do know it's there.

 

[Ledzep]

 

[Baron23]

View attachment 8787640

Thanks. But please note that the OP was not primarily talking about field results but that three other BC’s lined up pretty good w 4DOF being quite the erroneous outlier.

He did also note that AB, which more closely aligned w the other two BC’s, also closely matched his field experience.

On a separate note, I wonder WTF tests your app before you push it out.

WRT v1044 that you pushed out last week, I was out of town at a range and when trying to make any modifications to rifle data in a built gun (e.g. truing MV) 4DOF demanded I manually enter a bore diameter (even when using a bullet from the library and hence bore diameter is known).

This is also true when cloning a gun (and then editing the info) or building a new gun.

Selecting from the bore diameter pull down list (e.g. .264) did not save and therefore elevation was 0.0 not matter the entered range. Product just refused to work.

After cursing out Hornady for a hour or so as I tried over and over to select the required bore diameter, the only way I found to save the day was to use “Other” from the pull down list and manually enter .264”.

Yes, Hornady pushed v1049 out quickly to fix this incl populating bore diameter based on bullet selected from the library.

But the error was so incredibly obvious that if I was the program manager for this product I’d want to have a serious frakin’ talk with whoever generated the test cases for 4DOF new functionality and regression testing.

Just sort of undermines confidence in Hornady with this product.

 

[Ledzep]

Yeah that patch release was a problem... That's about all I'm going to say publicly about that...

And again, we're looking into the angle incline thing. 4DoF being different from a BC solver doesn't really alarm me in and of itself. 4DoF departing from reality does. We've tested it before and not found gross deviation, but that doesn't mean that something didn't change since we tested it last. We're in contact with the app developers to make sure everything is kosher on the inside, and we're planning a trip/test to verify real-world results. Sadly, we're in Nebraska, and it takes us 8-15 hours to get anywhere that has the terrain we need, and then it has to coincide with weather conditions conducive to testing, and align with work schedules...... Would love to do it today if it was a possibility.

 

[Baron23]

Yeah that patch release was a problem... That's about all I'm going to say publicly about tha

Yeah, I get it.