Advanced Marksmanship Wind effect on elevation and ..er... movers

[TheLimey]

On 4DOF 600 yards with 10mph wind from left made came back with come up 4.45 mils ...same speed wind from right came back as come up 4.26. Why is that?

What's the simplest way to calculate hold for a mover if I already know the distance to target and speed of the target?

 

[KnowNothing256]

The difference is due to aerodynamic jump. Has to do with the twist direction of the rifling.

I dunno about simplest, but the way I'd do it if I had time is:

- Determine time of flight (TOF) from your solver and known range
- Calculate distance traveled by the mover during that time
- Convert that distance to mils at that range

For example, 175 SMK at 2600 fps, no wind, 600 yds, mover traveling 10 mph:

- TOF is 0.884 seconds
- Mover is at 10 mph, so (0.884 sec)*(10 miles / hour)*(1 hour / 3600 seconds)*(1760 yards / mile) = 4.3 yards
- 4.3 / 600 * 1000 = 7.2 mils NOTE: At 600 yards, 1 mil is 0.6 yards (600/1000=0.6)


I think I did that right, somebody fact check me.

 

[KnowNothing256]

Tell you what, I can simplify it given the following assumptions:
- Your mover speed is given to you in X mph
- Your known range is in Y yards
- Your scope is mil/mil
- I did the calculation right the first time

Your hold in mils (with no wind) for the mover is:

489 * TOF * X / Y

If you wanna make it REAL simple, use 500 instead of 489. That's only a 2% error, and is absolutely how I'd do it now that I've looked at this haha.

 

[TheLimey]

Tell you what, I can simplify it given the following assumptions:
- Your mover speed is given to you in X mph
- Your known range is in Y yards
- Your scope is mil/mil
- I did the calculation right the first time

Your hold in mils (with no wind) for the mover is:

489 * TOF * X / Y

If you wanna make it REAL simple, use 500 instead of 489. That's only a 2% error, and is absolutely how I'd do it now that I've looked at this haha.

Thanks for going thru the cycles. Even I can execute that math! But where does the 489 number come from? Your bulleted assumptions are all correct.

 

[KnowNothing256]

The 489 comes from condensing all the constants in my original math into a single number:

1760/3600*1000 = 488.888...

 

[dgheriani]

That works great if you're given the mover speed (or are approximating it) in mph. If you need to determine the speed of the mover, get behind your scope and use your mil reticle to see how far it travels in a set time span (say 5s), divide the distance in mils by whatever time you used (5s in this case) to get a mover speed in mils/seconds and multiply that by your time of flight.

 

[TurboTrout]

That works great if you're given the mover speed (or are approximating it) in mph. If you need to determine the speed of the mover, get behind your scope and use your mil reticle to see how far it travels in a set time span (say 5s), divide the distance in mils by whatever time you used (5s in this case) to get a mover speed in mils/seconds and multiply that by your time of flight.

I take it this works the same if one substitutes mil for moa?

 

[dgheriani]

I take it this works the same if one substitutes mil for moa?

Sure, it would just be kinda clunky to do the math on the fly with fractions.

 

[TurboTrout]

Sure, it would just be kinda clunky to do the math on the fly with fractions.

So one couldn’t just do the same procedure but swap mil for moa on a FFP scope?

 

[acudaowner]

42

 

[SicVic]

TOF and speed estimation stirred in with a bunch of modern math is how I do it but in the end your wind calls have to be very accurate for any reliable feedback.

 

[KnowNothing256]

So one couldn’t just do the same procedure but swap mil for moa on a FFP scope?

That’s what he said, works exactly the same with MOA. Count how many MOA are traveled in a set time, then divide by the time to get your MOA per second, then multiply by TOF.

 

[Enough Said]

Our smooth pursuit neuropathway is the ultimate determiner and is why we cannot rely on math and time of flight alone.
It's your personal "lock time" and is not even consistent from from right-to-left compared to left-to-right pursuit unless trained.

Dig into this deep subject. It is very fascinating beyond engagement of movers with a firearm.