Range Report Horizontal Coriolis - Computing Average Velocity

[atlsniper6.5]

Howdy,

I'm working on an Excel sheet that will place Windage, Coriolis and Spin Drift in separate columns. I don't like that most ballistic software combines everything in to one "drift" column. Ballistic XLR is great, but last time I checked it requires you to use the G1 drag function, which obviously isn't the MOST accurate way of doing it for the OCD gun nerds out there (like me).

Question... The Horizontal Coriolis formula looks like this: (0.0000729*Range in ft^2*sin(Lat)) / Average Velocity

What is the formula for average velocity? I am guessing it is (distance in feet / time of flight in seconds) but want to make sure.

 

[EXTREMEPREJUDICE]

I am guessing it is (distance in feet / time of flight in seconds) but want to make sure.

That's a formula for average speed..........................see:Speed and Velocity

 

[atlsniper6.5]

Horizontal Coriolis - Computing Average Velocity

That's a formula for average speed..........................see:Speed and Velocity

Thanks, so wouldn't "displacement"
be equal to range in feet for our purposes? If not, how do you determine the value for displacement? You can't really plug 1000 fps East in to a formula. I think speed and velocity are equal for the purpose of this formula.


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[tobias]

Howdy,

Question... The Horizontal Coriolis formula looks like this: (0.0000729*Range in ft^2*sin(Lat)) / Average Velocity

Formula for what? The unit is ft*s, that doesn't make sense.

 

[atlsniper6.5]

Formula for what? The unit is ft*s, that doesn't make sense.

I'm not sure what you're asking, brother. I believe the formula for Average Velocity is (range in feet / time of flight in seconds). Just trying to confirm it so my inputs are correct.


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[OF&B]

Howdy,

I'm working on an Excel sheet that will place Windage, Coriolis and Spin Drift in separate columns. I don't like that most ballistic software combines everything in to one "drift" column. Ballistic XLR is great, but last time I checked it requires you to use the G1 drag function, which obviously isn't the MOST accurate way of doing it for the OCD gun nerds out there (like me).

Question... The Horizontal Coriolis formula looks like this: (0.0000729*Range in ft^2*sin(Lat)) / Average Velocity

What is the formula for average velocity? I am guessing it is (distance in feet / time of flight in seconds) but want to make sure.

Litz gives that equation as 0.00007292 radians/sec * Range in ft * sin(Lat) * TOF, with Time Of Flight in seconds.

Using Range / TOF as the Average Velocity gives the same result if you substitute TOF = Range / Average Velocity into the Litz equation.

So Yes, Average Velocity is Range / TOF in your equation.

For a 175 grain smk with a muzzle velocity of 2650 fps, it's a 1.692 second TOF to 3000 ft at a latitude of 39 degrees north

0.00007292 rad/sec * 3000 ft * sin(39) * 1.692 sec = 0.2329 ft, 2.8"

Shooter gave 2.4"

Using your formula

0.00007292 rad/sec * 3000 ft * 3000 ft * sin(39) / (3000 ft / 1.692 sec) = 0.2329 ft, 2.8"

 

[atlsniper6.5]

Litz gives that equation as 0.00007292 radians/sec * Range in ft * sin(Lat) * TOF, with Time Of Flight in seconds.

Using Range / TOF as the Average Velocity gives the same result if you substitute TOF = Range / Average Velocity into the Litz equation.

So Yes, Average Velocity is Range / TOF in your equation.

For a 175 grain smk with a muzzle velocity of 2650 fps, it's a 1.692 second TOF to 3000 ft at a latitude of 39 degrees north

0.00007292 rad/sec * 3000 ft * sin(39) * 1.692 sec = 0.2329 ft, 2.8"

Shooter gave 2.4"

Using your formula

0.00007292 rad/sec * 3000 ft * 3000 ft * sin(39) / (3000 ft / 1.692 sec) = 0.2329 ft, 2.8"

Thanks, sir!


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[TiroFijo]

Just remember coriolis drift depends on angle of repose of the particular bullet (that also depends on rifling twist and other factors), so you are merely estimating with this formula...

 

[atlsniper6.5]

For running dope straight from a device in the field, I want them combined.

But ya, for planning and making printed dope cards I also would like the software to give an option to have separate columns. I usually, run a zero wind value with SD on, the wind value with SD OFF.. Then manually combine the columns into a separate sheet to make my cards.

Of course it isn't perfect as in this case I have Drop, SD, 10mph 90wind value... But that way when estimating, I can double, 1/4, etc wind values -- then quickly add of subtract SD. I attach these very minimalistic cards to the mags. I use them as a backup and sometimes as reference if my ballistic solution looks funky. As an example, my 338 and 7MM can look fairly similar out to about 2K (wind being the easiest give away). I might load the wrong gun profile in my solver, but the cards on the mag generally can provide a double check.

For me coriolis has to many variables to print out and attach to the magazine- as does air density. But with air density I can usually pre print out a card that gets me in the ball park depending on were I plan on being..

Here is one card-

Are you planning on running Excel in the field?


Jt

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Thanks for the info. You've definitely given me some ideas. I will probably do a little bit of both (Excel vs. Print Outs). Honestly, I'm not really sure what I want this to look like yet. I guess the end goal is to develop a dope card book with a reliable set of constants that I can access/tweak easily without having to do all the math in the field (when the battery on the iPad goes out).


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[Analytical Rifleist]

altsniper:

OF&B has listed the correct formula, but I fear the issue of velocity may remain. For the vacuum trajectory the muzzle velocity is correct but the air through which the bullet moves has a local velocity, thus should effectively create a wind. The Didion model for wind drift partitions the flight into vacuum component and drag component, and applies local wind velocity to the drag component. So it might be that the most accurate calculation is to use simply the muzzle velocity. It may or may not be significant that McCoy's examples in Modern Exterior Ballistics uses muzzle velocity when it would be just as easy to use average velocity. Or I may not be thinking correctly. I would like to see more discussion on this.

Thank you for asking the question.

 

[Analytical Rifleist]

To altsniper and OF&B:

Compared to all the references I have handy, the equation listed with the constant 7.3 e-5 is missing a factor of two.
It is interesting that dropping the factor of two and using total flight time should give results very similar to
using 2 * 7.3e-5 and the vacuum flight time.

 

[atlsniper6.5]

To altsniper and OF&B:

Compared to all the references I have handy, the equation listed with the constant 7.3 e-5 is missing a factor of two.
It is interesting that dropping the factor of two and using total flight time should give results very similar to
using 2 * 7.3e-5 and the vacuum flight time.

I guess at the end of the day the only thing that matters is if the error between formulas is enough to be greater than shooter/turret error. Still fun to debate this stuff though


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[pdogsbeware]

Throw a tennis ball up in the air. See how it moves horizontally? Oh wait, it doesn't? Stop worrying about coriolis.

 

[spamassassin]

I already did this. Check out ballisticxlr.com it's free and supported for free.

 

[Analytical Rifleist]

Correction to Correction to ......

Howdy,


Question... The Horizontal Coriolis formula looks like this: (0.0000729*Range in ft^2*sin(Lat)) / Average Velocity

Altsniper6.5
I have recently grunted through McCoy and others, and I now believe your equation should not have a factor of two, but would be more accurate with muzzle velocity. This is more hunch than analysis. But in the scheme of things it is hardly a big deal. The Lapua 250 gr at 2970 fps, showing 256 in. drop at 1000 yds has less than 2in. drift at 45 degrees NL, and less in Texas. The basic physics is that the trajectory rotates with time (think Foucault pendulum) so the exact calculation is quite doable if it needs doing.

 

[Kirkd]

Horizontal Coriolis - Computing Average Velocity

Howdy,

I'm working on an Excel sheet that will place Windage, Coriolis and Spin Drift in separate columns. I don't like that most ballistic software combines everything in to one "drift" column. Ballistic XLR is great, but last time I checked it requires you to use the G1 drag function, which obviously isn't the MOST accurate way of doing it for the OCD gun nerds out there (like me).

Question... The Horizontal Coriolis formula looks like this: (0.0000729*Range in ft^2*sin(Lat)) / Average Velocity

What is the formula for average velocity? I am guessing it is (distance in feet / time of flight in seconds) but want to make sure.

Why reinvent the wheel? This has already been done is available for FREE. I enter my info and print the chart out.

See below.

Sorry to bring this back from the nearly dead.

The Ballistic_XLR spreadsheet mentioned above by Kirkd is maintained by me. You can get free support at Ballistic_XLR | Ballistics, Long Range Precision Shooting and Gun Rights, email to [email protected] or PM on YouTube or comment on a video or any number of other ways.

As a matter of pride and honesty, let me be clear that this is a modification of the Pejsa spreadsheet with consultation and table layout from TiborasaurusRex and others. I did a ton of work on it but others started it.

The latest version as of this writing is v3.0.5 (about to publish 3.0.7). It now supports full metric units of measure for those in zip code foreign. I rarely make it to the hide (work, shooting, Ballistic_XLR keep me busy). If anyone has a feature request or bug report please contact me outside the hide (email is best) so I don't leave you hanging.

Each version usually gets a little video introduction to the differences. I trust that the guys here should know how to fill it out but if you need help please don't hesitate to ask. https://www.youtube.com/watch?v=3LQyBEsVcZU this is the video for the latest update.

Ballistic_XLR will always be free to download and general support is free.

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