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.