- Thread starter HumbleEinstein
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For me this worked just as fine as it did at our own flat ranges. For 308 i found that for calibration a range of 850-1000m worked best to get the most accuracte comparison between software predictions and real life target elevations.

I used the bc calibration, but the muzzlevelocity will give just as good results.

After calibration i was almost deadon at all ranges from 540 out to 1606m, for elevation, with an accuracy of .1 mil...windage however......

Just put in as much accurate info as possibe when your calibrating; range, heading, inclination, pressure, temp, moist etc.

R

I use an angle indicator because that's what my Iphone ap needs as an input.

My geometry is a little rusty, but the cosine factor is multplied by the your dope. So if your dope is 10.0 mils at a given distance, and your cosine is 0.87, your dope woudl be 8.7. Oversimplified to be sure. Again, I use an angle indicator.

Correct, had a brain fart

R

That is not correct. Correcting range by the cosine of the angle is a 'quick fix', and only an approximation. It's referred to as "The Riflemans Rule" The improved version of this rule uses the cosine to correct the elevation setting, which is close, but still not exact.

If the target angle exceeds 5 degrees and the range exceeds 600 yards, you might not want to try and use that data point as a correction factor, but you can use it to check if the current model is correct by seeing if entering the range and angle give the correct setting as actually used.

For further information on this subject, see Inclined Fire on the Sierra Bullets ballistics website.

exterior ballistics

That was precisely my concern. It seems to me that using angled shot DOPE might be inherently flawed for the purpose of truing common ballistic software. Thank you for the information.

That is not correct. Correcting range by the cosine of the angle is a 'quick fix', and only an approximation. It's referred to as "The Riflemans Rule" The improved version of this rule uses the cosine to correct the elevation setting, which is close, but still not exact.

If the target angle exceeds 5 degrees and the range exceeds 600 yards, you might not want to try and use that data point as a correction factor, but you can use it to check if the current model is correct by seeing if entering the range and angle give the correct setting as actually used.

For further information on this subject, see Inclined Fire on the Sierra Bullets ballistics website.

exterior ballistics

If I understand the problem correctly, you want to true your ballistic curve, but only have an inclined range to do it, right?That was precisely my concern. It seems to me that using angled shot DOPE might be inherently flawed for the purpose of truing common ballistic software. Thank you for the information.

Estimating the "flat" dope out of inclined fire results may introduce significant errors; basically, you would be "reversing" one of the known rules of thumb (such as Rifleman's Rule) with all associated inaccuracies.

If you still want to go that way, your best bet is to reverse the "Increasingly Improved Rifleman's Rule" -- mil clicks version or MOA clicks version, depending on your scope. In other words, add [X] clicks per [Y] degrees (see the method description), then

This being said, the purpose of truing is to calibrate the drag curve of a particular bullet. With common bullets, chances are that someone (with more resources and knowledge) has already done it before (e.g., the AB software has excellent custom curves researched by Bryan Litz). In this case, "truing" is basically knowing your V0 with enough precision, knowing the V0/temperature dependence, and checking that predictions correspond to reality.

I totally second CoryT's opinion re: "use it to check if the current model is correct".

AB solver actually does the 3-DOF model calculations of the "true" trajectory, which is very, very close to reality (provided that actual input data, incl. the bullet drag model, is correct). The "Rifleman's Rule" is total crap beyond 400 m.

Correct. I guess I'll use the match to the confirm predictions of the software. I'll have to collect data to true (if necessary) at a future time.If I understand the problem correctly, you want to true your ballistic curve, but only have an inclined range to do it, right?

Estimating the "flat" dope out of inclined fire results may introduce significant errors; basically, you would be "reversing" one of the known rules of thumb (such as Rifleman's Rule) with all associated inaccuracies.

If you still want to go that way, your best bet is to reverse the "Increasingly Improved Rifleman's Rule" -- mil clicks version or MOA clicks version, depending on your scope. In other words, add [X] clicks per [Y] degrees (see the method description), thendivide(not multiply) the result by cosine. Up to 800 m / 40 degrees you should stay within ±1 click from truth (unless using a very exotic calibre).

This being said, the purpose of truing is to calibrate the drag curve of a particular bullet. With common bullets, chances are that someone (with more resources and knowledge) has already done it before (e.g., the AB software has excellent custom curves researched by Bryan Litz). In this case, "truing" is basically knowing your V0 with enough precision, knowing the V0/temperature dependence, and checking that predictions correspond to reality.

I totally second CoryT's opinion re: "use it to check if the current model is correct".

So, is it correct to say that the AB Kestrel can be used to "true" when shooting at an angle since the truing function uses the difference between the Kestrel calculated elevation and the actual elevation.AB solver actually does the 3-DOF model calculations of the "true" trajectory, which is very, very close to reality (provided that actual input data, incl. the bullet drag model, is correct). The "Rifleman's Rule" is total crap beyond 400 m.

Yes and no.So, is it correct to say that the AB Kestrel can be used to "true" when shooting at an angle since the truing function uses the difference between the Kestrel calculated elevation and the actual elevation.

You cannot really use it to create a custom drag curve for a bullet, at least not directly.

But you can see if the model that you are using is correct or not.

Not true, you can create custom curves.Yes and no.

You cannot really use it to create a custom drag curve for a bullet, at least not directly.

But you can see if the model that you are using is correct or not.

I'd love to know how to do that -- that is, how to build a custom drag model for a bullet out of measured slope dope with significant angles of inclination.Not true, you can create custom curves.

Any links to documentation, guides, resources, even hard copy books?

Because, short of writing a custom ballistic solver software, I see no easy way -- but maybe I simply fail to see the obvious, my brain is not what it used to be.

(I am not afraid of math, and have some notions of external ballistics, so any level of technical detail is ok.)

On a another note, would I need to calibrate my DSF if I'm already using one of the custom curves?