Applied Ballistic App Environmental Confusion and Other Questions

[BoltBandit]

I have a few questions about the Applied Ballistics App and how it calculates as well as recommendations for making DOPE cards.

Here it goes. In preferences the AB app is set to use Density Altitude to calculate. (I read somewhere that a 2500 DA calculated with one set of data is different than shooting in a 2500 DA using a different set of data. i.e. low altitude and high temp vs high altitude and low temp. Is this true?) Anyway, I'm setting my target distance to 1,000 yards with 0 wind coming in at 3 O'clock. Selecting the gun and then the bullet, I get to the Environment Screen.
Distance - 1,000 yards
DA defaults to 0 ft
Temperature defaults to 59F
Wind Speed is 0 mph.

This results in U8.1 mils in elevation. If I change the temperature to 0F, the elevation adjustment changes to U8.6 mils.

If DA is a calculation that is in part based on Temperature, then a change in temperature should change the DA. My guess is the DA isn't auto-updating when temperature is changed?

So the question is this. If I'm inputting the DA from a Kestral Sportsman, do I need to adjust the temperature in the AB app as well to get a proper firing solution?

The second half of my thread is regarding making DOPE cards and accounting for spin drift.

Again, using the AB app. Distance is set to 1,000 yards, DA = 0 ft, and Temp = 0F. With 0 wind and spin drift enabled, I need to adjust windage L.02 at a 1,000 yards. My assumption is that at 1,000 yards with the above environmentals, 0.2 mils of adjustment is required to account for spin drift. Lets mix it up. All things being the same except if I add a 10mph wind at 90 degrees, and turn OFF spin drift, the correction for a 90 degree wind is R2.1 mils. The adjustment for an opposing 10 mph wind at a 270 degree angle is the exact same at L2.1 mils. Time to make it interesting. If I turn ON spin drift, a 10 mph wind at 90 degrees requires a correction of R1.9 mils. However, a 10 mph wind at 270 degrees requires a correction of L2.2! So with spin drift turned on, it makes sense that a 90 degree wind would go from R2.1 to R1.9, a 0.2 adjustment, exactly what is called for when accounting for spin drift in a zero wind condition. However, with a 270 degree wind, the adjustment for spin drift is only 0.1 mils. Is this correct? I would think the correction for a 270 degree wind would be L2.3, to mirror the adjustment for spin drift in a zero wind condition.

I'm making DOPE cards based on DA with a low wind value and a high wind value of 5 mph and high of 10mph. I color coded the cells light blue to notate a 0.1 shift for spin drift for each applicable distance, and color coded cells light green for cells corresponding to a distance that requires a 0.2 shift for spin drift. But if I use this logic at 1,000 yards with a 10 mph wind at 270 degrees and apply a 0.2 shift in POI, then I will be 0.1 mils too far left compared to what the ballistics calculator spits out. Which is correct.

And finally! When making a wind call, when do I apply an adjustment for spin drift. Before or after I've corrected for wind angle?

For example. 1,000 yards with a 10mph wind coming in at 45 dgrees. The correction for a 90 degree 10 mph wind with NO spin drift calculated is R2.1. The coefficient for a 45 degree wind is .71, and the adjustment for spin drift is L0.2 mils. So the math can be done one of two ways. Account for spin drift THEN mulitply that number by the angle coefficient, or multiply the wind adjustment by the angle coefficient, THEN apply the correction for spin drift. The math is as follows, which is correct.

(R2.1 + L.02)*.71 = R1.349
or
(R2.1*.71)+L0.2 = R1.291

I know this is splitting hairs and equates to a 1.8" difference in POI. But theoretically, which is correct.

 

[pyrotechnic]

If DA is a calculation that is in part based on Temperature, then a change in temperature should change the DA. My guess is the DA isn't auto-updating when temperature is changed?

I don't know how AB "calculates" spin drift so I can't help with the second part of the question, but my gut tells me you would want to calculate your wind drift, then add/subtract your spin drift to it.

I'll take a stab at the quoted part though.

A G funtion is essentially a set of drag coefficients vs Mach numbers. In an ideal gas (this assumption is used for air) the speed of sound depends solely on temperature.

So while your air densities may be the same at the selected density altitude your Mach number will be slightly different, resulting in a slightly different drag coefficient being referenced as the solver steps through it's iterations.

 

[BoltBandit]

Hmmmm, that makes sense. So would a custom curve negate this since it’s based on doplar?

 

[pyrotechnic]

I don't believe it would as the custom curve would also be a set of Drag coefficients vs Mach numbers. The curve will more closely match your projectile vs just scaling the G1 or G7 curve by your BC. But you're Mach number will still be based off of the air temp.

I used DA for quick reference cards I Velcro to my rifle and can swap out for changing conditions. But if I have time, I'll use my app with correct temperature and station pressure inputs.

 

[_Windrider_]

I have a few questions about the Applied Ballistics App and how it calculates as well as recommendations for making DOPE cards.

Here it goes. In preferences the AB app is set to use Density Altitude to calculate. (I read somewhere that a 2500 DA calculated with one set of data is different than shooting in a 2500 DA using a different set of data. i.e. low altitude and high temp vs high altitude and low temp. Is this true?) Anyway, I'm setting my target distance to 1,000 yards with 0 wind coming in at 3 O'clock. Selecting the gun and then the bullet, I get to the Environment Screen.
Distance - 1,000 yards
DA defaults to 0 ft
Temperature defaults to 59F
Wind Speed is 0 mph.

This results in U8.1 mils in elevation. If I change the temperature to 0F, the elevation adjustment changes to U8.6 mils.

If DA is a calculation that is in part based on Temperature, then a change in temperature should change the DA. My guess is the DA isn't auto-updating when temperature is changed?

So the question is this. If I'm inputting the DA from a Kestral Sportsman, do I need to adjust the temperature in the AB app as well to get a proper firing solution?

The second half of my thread is regarding making DOPE cards and accounting for spin drift.

Again, using the AB app. Distance is set to 1,000 yards, DA = 0 ft, and Temp = 0F. With 0 wind and spin drift enabled, I need to adjust windage L.02 at a 1,000 yards. My assumption is that at 1,000 yards with the above environmentals, 0.2 mils of adjustment is required to account for spin drift. Lets mix it up. All things being the same except if I add a 10mph wind at 90 degrees, and turn OFF spin drift, the correction for a 90 degree wind is R2.1 mils. The adjustment for an opposing 10 mph wind at a 270 degree angle is the exact same at L2.1 mils. Time to make it interesting. If I turn ON spin drift, a 10 mph wind at 90 degrees requires a correction of R1.9 mils. However, a 10 mph wind at 270 degrees requires a correction of L2.2! So with spin drift turned on, it makes sense that a 90 degree wind would go from R2.1 to R1.9, a 0.2 adjustment, exactly what is called for when accounting for spin drift in a zero wind condition. However, with a 270 degree wind, the adjustment for spin drift is only 0.1 mils. Is this correct? I would think the correction for a 270 degree wind would be L2.3, to mirror the adjustment for spin drift in a zero wind condition.

I'm making DOPE cards based on DA with a low wind value and a high wind value of 5 mph and high of 10mph. I color coded the cells light blue to notate a 0.1 shift for spin drift for each applicable distance, and color coded cells light green for cells corresponding to a distance that requires a 0.2 shift for spin drift. But if I use this logic at 1,000 yards with a 10 mph wind at 270 degrees and apply a 0.2 shift in POI, then I will be 0.1 mils too far left compared to what the ballistics calculator spits out. Which is correct.

And finally! When making a wind call, when do I apply an adjustment for spin drift. Before or after I've corrected for wind angle?

For example. 1,000 yards with a 10mph wind coming in at 45 degrees. The correction for a 90 degree 10 mph wind with NO spin drift calculated is R2.1. The coefficient for a 45 degree wind is .71, and the adjustment for spin drift is L0.2 mils. So the math can be done one of two ways. Account for spin drift THEN multiply that number by the angle coefficient, or multiply the wind adjustment by the angle coefficient, THEN apply the correction for spin drift. The math is as follows, which is correct.

(R2.1 + L.02)*.71 = R1.349
or
(R2.1*.71)+L0.2 = R1.291

I know this is splitting hairs and equates to a 1.8" difference in POI. But theoretically, which is correct.

well first off at 0 degrees temp your MV is gonna be WAY OFF.

Second 0 DA and ) degrees is the equivalent of -4000 feet elevation.

third, turn off the noise. Set wind 1 to zero and use only wind 2. Turn SD off, and finally set your lattitude to 0. now build your cards. then go shoot and verify and track your dope. the differences )if any) is the SD and AJ (coriolis is a non factor).

 

[BoltBandit]

well first off at 0 degrees temp your MV is gonna be WAY OFF.

Second 0 DA and ) degrees is the equivalent of -4000 feet elevation.

third, turn off the noise. Set wind 1 to zero and use only wind 2. Turn SD off, and finally set your lattitude to 0. now build your cards. then go shoot and verify and track your dope. the differences )if any) is the SD and AJ (coriolis is a non factor).

So why would temp affect DA if the temp is part of the DA calculation? That’s what is confusing me.

 

[_Windrider_]

So why would temp affect DA if the temp is part of the DA calculation? That’s what is confusing me.

Well it affects your MV too.
I suggest turning off DA and using the actual atmospherics. See if that changes anything.

 

[DocUSMCRetired]

I have answered in red.

I have a few questions about the Applied Ballistics App and how it calculates as well as recommendations for making DOPE cards.

Here it goes. In preferences the AB app is set to use Density Altitude to calculate. (I read somewhere that a 2500 DA calculated with one set of data is different than shooting in a 2500 DA using a different set of data. i.e. low altitude and high temp vs high altitude and low temp. Is this true?) This is true, and why it is always best to use Actual Temp, Station Pressure, and set humidity to 50% unless shooting ELR. Barometric Pressure has its own set of inaccuracies. Anyway, I'm setting my target distance to 1,000 yards with 0 wind coming in at 3 O'clock. Selecting the gun and then the bullet, I get to the Environment Screen.
Distance - 1,000 yards
DA defaults to 0 ft
Temperature defaults to 59F
Wind Speed is 0 mph.

This results in U8.1 mils in elevation. If I change the temperature to 0F, the elevation adjustment changes to U8.6 mils.

If DA is a calculation that is in part based on Temperature, then a change in temperature should change the DA. My guess is the DA isn't auto-updating when temperature is changed? The speed of sound is temperature dependent and has a direct correlation on the current drag experienced by the bullet. The transition from supersonic to subsonic being a very critical piece of data.

So the question is this. If I'm inputting the DA from a Kestral Sportsman, do I need to adjust the temperature in the AB app as well to get a proper firing solution? You need to use Temp, and Station Pressure directly off the device. This will be the most accurate.

The second half of my thread is regarding making DOPE cards and accounting for spin drift.

Again, using the AB app. Distance is set to 1,000 yards, DA = 0 ft, and Temp = 0F. With 0 wind and spin drift enabled, I need to adjust windage L.02 at a 1,000 yards. My assumption is that at 1,000 yards with the above environmentals, 0.2 mils of adjustment is required to account for spin drift. Lets mix it up. All things being the same except if I add a 10mph wind at 90 degrees, and turn OFF spin drift, the correction for a 90 degree wind is R2.1 mils. The adjustment for an opposing 10 mph wind at a 270 degree angle is the exact same at L2.1 mils. Time to make it interesting. If I turn ON spin drift, a 10 mph wind at 90 degrees requires a correction of R1.9 mils. However, a 10 mph wind at 270 degrees requires a correction of L2.2! So with spin drift turned on, it makes sense that a 90 degree wind would go from R2.1 to R1.9, a 0.2 adjustment, exactly what is called for when accounting for spin drift in a zero wind condition. However, with a 270 degree wind, the adjustment for spin drift is only 0.1 mils. Is this correct? I would think the correction for a 270 degree wind would be L2.3, to mirror the adjustment for spin drift in a zero wind condition. You also need to account for rounding. The display is giving you only one decimal place without the entire solution. You can often see this by going from 1 mph to 10 mph as well.

I'm making DOPE cards based on DA with a low wind value and a high wind value of 5 mph and high of 10mph. I color coded the cells light blue to notate a 0.1 shift for spin drift for each applicable distance, and color coded cells light green for cells corresponding to a distance that requires a 0.2 shift for spin drift. But if I use this logic at 1,000 yards with a 10 mph wind at 270 degrees and apply a 0.2 shift in POI, then I will be 0.1 mils too far left compared to what the ballistics calculator spits out. Which is correct.

And finally! When making a wind call, when do I apply an adjustment for spin drift. Before or after I've corrected for wind angle? Let the software do it for you.

For example. 1,000 yards with a 10mph wind coming in at 45 dgrees. The correction for a 90 degree 10 mph wind with NO spin drift calculated is R2.1. The coefficient for a 45 degree wind is .71, and the adjustment for spin drift is L0.2 mils. So the math can be done one of two ways. Account for spin drift THEN mulitply that number by the angle coefficient, or multiply the wind adjustment by the angle coefficient, THEN apply the correction for spin drift. The math is as follows, which is correct.

(R2.1 + L.02)*.71 = R1.349
or
(R2.1*.71)+L0.2 = R1.291

I know this is splitting hairs and equates to a 1.8" difference in POI. But theoretically, which is correct.

 

[DocUSMCRetired]

Hmmmm, that makes sense. So would a custom curve negate this since it’s based on doplar?

A CDM will not negate the effect temperature has on the speed of sound. A CDM will provide far more accurate predictions because you are not basing the performance on a standard, but using the bullets actual flight model as measured. I believe you would benefit from the following articles:

1) https://appliedballisticsllc.com/2019/11/11/aerodynamic-drag-modeling-for-ballistics/

2) https://appliedballisticsllc.com/20...drag-measurement-and-modeling-for-small-arms/

3) https://appliedballisticsllc.com/2019/11/08/transonic-effects-on-bullet-stability-bc/

 

[Jack Master]

I've ventured through these waters too to fill out a good DA card.

So the question is this. If I'm inputting the DA from a Kestral Sportsman, do I need to adjust the temperature in the AB app as well to get a proper firing solution?

If you are making a DA dope card you'll need to understand you are going to have some general errors any way you approach it. Rounding of DA, temp and spin drift are the top things.

Dealing with Temperature
As Doc suggested above it is the most accurate to use the Station pressure and temperature, but to do a full spectrum of temperature and pressures on a chart takes a lot of cards so we are back to calculating DA to simplify the data. But. Yes, we need to be conscious of changes in our muzzle velocity and changing speed of sound due to temperature changes. To do this I apply a correction factor to my calculated DA. I add or subtract 500DA for every 15 degrees of temperature change from my data. If the DA column I am using was created with 60 degrees and its 90 the day i am shooting I will add 1000ft (30 deg change) to my DA. similarly I will subtract DA if its colder.
Have a read here - Making Ballistic Cards Using Density Altitude - Lindy

Dealing with Spin Drift
I've played with a lot of the numbers and apply my own spin drift. I never had spin drift in a dope card data. I use 10% of my come up. A lot of programs use 20%. Its not perfect but atleast I am accounting for it. 1000yds dial is is less than 10 mils--> this means less than 0.1 mils spindrift.

And finally! When making a wind call, when do I apply an adjustment for spin drift. Before or after I've corrected for wind angle?

Always - make the wind call. Then add the spin drift. This is correct --> (R2.1*.71)+L0.2 = R1.291
spin drift has nothing to do with the wind direction or speed, keep them separate and add them together in the last step.

 

[DocUSMCRetired]

@BoltBandit

I think this is what you are actually wanting: https://www.accuracy1st.com/store/catDetail.cfm?catID=58 These are made using our CDMs and the AB Analytics software. So they essentially are a byproduct of our Engine.