Thread: Truing a Ballistic Calculator

https://www.snipershide.com/precisio...aponized-math/
Worked for me

Originally Posted by mikee

https://www.snipershide.com/precisio...aponized-math/
Worked for me

Thats a great article, read it a few weeks ago whilst on holiday . . . BUT despite reading it (and a 22 version) a couple of times I still don't "get it" - I flunked maths and chemistry more than 40 years ago but can still do trig and stats for everyday purposes so I dunno - call me a dunce.

Originally Posted by stagstalker

A drag model calculated and proven by doppler radar does not get changed. MV is the variable factor not the drag model.

Of course it does.
AB have even seen the change in bc over the life of a barrel so saying everyone's guns will shoot the same bullet at the same bc is crazy.

@Tentman what calculator are you using?
I will true mv out as far as i can upto about 7-800m and bc at 1000-1400.(for a decent 6.5etc)
Once both are done it might take a little fiddle to get the last .2mil to line up.

I'm using Strelok (I'm cheap) and I think I've got it sorted now - Saturday will tell a story! I can only shoot to 600Y (549M) here so have one hand tied behind my back (in addition to my usual handicaps)

I am not sure if some of you are trolling here.........

When it comes to truing I would refer to the "Grandfather of Truing" (Todd Hodnett) in the first instance:

https://www.youtube.com/watch?v=KaOEyGeWDdk

Secondly, what is wrong with this article?

https://www.snipershide.com/precisio...aponized-math/

1. Ignores the effect of density altitude. Due to the design of the protracted methodology, there is every likelihood that the density altitude will change over the duration of the truing exercise. During the recent Alpine Long Range Shooting Comp (ALRSC) there was a sharp weather change over 15min. For me, this resulted in a 0.3 mil change in elevation at 800m shooting the 260 REM when I updated the environment in my Kestrel 5700. By ignoring DA and conducting a protracted truing process, you run the risk of corrupting your data.

2. Ignores the effect of MV Migration - very important when it comes to magnums. A rifle's MV will not remain constant over the life of the barrel, even if all other variables remain constant. For example, over the first 150-200 rounds of a 338LM's life you will observe approximately 50fps in MV migration (eg. 2700 fps to 2750 fps). Then pending cleaning regime, you may observe drastic MV migration over the first 50 rounds following a robust clean prior to settling down. Once again, prior to the ALRSC I trued the 260 (CAL MV) and expected my average MV to change over the course of the match because it was a new barrel - which it did! When engaging the target at 1000m I noticed that I was approx 0.2mils high and I updated the Kestrel accordingly. But by conducting a protracted truing process as described in the article, you are once again exposing yourself to the risk of creating corrupted data as you MV may not be consistent between all of the recommended 100m/yd increments.

3. Adjusting both MV and BC pre trans is asking for trouble. I don't think I need to go too deep on this, especially if you take the above into consideration and do the math on the compounding effect. Furthermore, if you start playing with both MV and BC in your Kestrel for what would be a adhoc CAL MV process, it will most likely throw out your post trans true - CAL DSF. Listen to Grandad (Todd) and just adjust your MV at approx Mach 1.2.

4. Their math is poor. I quote:

"A 308 going about 2550fps is about 1 mil every 100 yards from 400 to 700 yards, give or take a tenth or two"

So plugging that into the Kestrel with the following parameters; 175gr SMK, 2550fps, DA = 716ft, G7 = 0.243 we get the following elevation holds:

100yd = 0.00mils
200yd = 0.61mils
300yd = 1.49mils
400yd = 2.51mils (delta = 1.02mils)
500yd = 3.67mils (delta = 1.16mils)
600yd = 4.98mils (delta = 1.31mils)
700yd = 6.47mils (delta = 1.49mils)
800yd = 8.16mils

When truing, you want to be as accurate as possible. There are times for gross generalisations in LR/ELR shooting. Truing is not one of them.

5. Aerodynamic Jump (AJ) matters. I quote:

"An impact using 4.2 Mils doesn’t need to include Spindrift, Coriolis, or Aerodynamic Jump, because 4.2 is the final answer; it’s not 4.2 plus, it’s just 4.2; that is what we true too."

The author is not really clear in what they are saying here so I will emphasise - account for AJ! Truing is all about the vertical component of the trajectory and we need to account for the variables that affect this to a quantifiable degree that matters. For example, using the gun profile provided above (175gr SMK, 2550fps, DA = 716ft, G7 = 0.243), this setup will approx 0.1 mils of AJ per 6mph of wind. Therefore, if you are truing in 12mph wind, you will have 0.2mils deviation high or low pending which way the wind is coming from. This delta needs be removed from the calibration input.

In summary, keep your truing methodology as simple and accurate as possible. And like the Grandfather of Truing says - "know what matters".

JT

Originally Posted by JT_NZ

I am not sure if some of you are trolling here.........

When it comes to truing I would refer to the "Grandfather of Truing" (Todd Hodnett) in the first instance:

https://www.youtube.com/watch?v=KaOEyGeWDdk

Secondly, what is wrong with this article?

https://www.snipershide.com/precisio...aponized-math/

1. Ignores the effect of density altitude. Due to the design of the protracted methodology, there is every likelihood that the density altitude will change over the duration of the truing exercise. During the recent Alpine Long Range Shooting Comp (ALRSC) there was a sharp weather change over 15min. For me, this resulted in a 0.3 mil change in elevation at 800m shooting the 260 REM when I updated the environment in my Kestrel 5700. By ignoring DA and conducting a protracted truing process, you run the risk of corrupting your data.

2. Ignores the effect of MV Migration - very important when it comes to magnums. A rifle's MV will not remain constant over the life of the barrel, even if all other variables remain constant. For example, over the first 150-200 rounds of a 338LM's life you will observe approximately 50fps in MV migration (eg. 2700 fps to 2750 fps). Then pending cleaning regime, you may observe drastic MV migration over the first 50 rounds following a robust clean prior to settling down. Once again, prior to the ALRSC I trued the 260 (CAL MV) and expected my average MV to change over the course of the match because it was a new barrel - which it did! When engaging the target at 1000m I noticed that I was approx 0.2mils high and I updated the Kestrel accordingly. But by conducting a protracted truing process as described in the article, you are once again exposing yourself to the risk of creating corrupted data as you MV may not be consistent between all of the recommended 100m/yd increments.

3. Adjusting both MV and BC pre trans is asking for trouble. I don't think I need to go too deep on this, especially if you take the above into consideration and do the math on the compounding effect. Furthermore, if you start playing with both MV and BC in your Kestrel for what would be a adhoc CAL MV process, it will most likely throw out your post trans true - CAL DSF. Listen to Grandad (Todd) and just adjust your MV at approx Mach 1.2.

4. Their math is poor. I quote:

"A 308 going about 2550fps is about 1 mil every 100 yards from 400 to 700 yards, give or take a tenth or two"

So plugging that into the Kestrel with the following parameters; 175gr SMK, 2550fps, DA = 716ft, G7 = 0.243 we get the following elevation holds:

100yd = 0.00mils
200yd = 0.61mils
300yd = 1.49mils
400yd = 2.51mils (delta = 1.02mils)
500yd = 3.67mils (delta = 1.16mils)
600yd = 4.98mils (delta = 1.31mils)
700yd = 6.47mils (delta = 1.49mils)
800yd = 8.16mils

When truing, you want to be as accurate as possible. There are times for gross generalisations in LR/ELR shooting. Truing is not one of them.

5. Aerodynamic Jump (AJ) matters. I quote:

"An impact using 4.2 Mils doesn’t need to include Spindrift, Coriolis, or Aerodynamic Jump, because 4.2 is the final answer; it’s not 4.2 plus, it’s just 4.2; that is what we true too."

The author is not really clear in what they are saying here so I will emphasise - account for AJ! Truing is all about the vertical component of the trajectory and we need to account for the variables that affect this to a quantifiable degree that matters. For example, using the gun profile provided above (175gr SMK, 2550fps, DA = 716ft, G7 = 0.243), this setup will approx 0.1 mils of AJ per 6mph of wind. Therefore, if you are truing in 12mph wind, you will have 0.2mils deviation high or low pending which way the wind is coming from. This delta needs be removed from the calibration input.

In summary, keep your truing methodology as simple and accurate as possible. And like the Grandfather of Truing says - "know what matters".

JT

That's what I meant!

Sent from my SM-G950F using Tapatalk

What this man said ^ @JT_NZ

I read that article and just thought wow, that was one way of making what is a simple process a whole lot longer and more complicated and not even necessarily correct after all that!

If adjusting BC to true was a thing then people like Todd Hodnett and snipers all over the world would do it, buuut, they don’t.

Hey thanks for that @JT_NZ , I watched the video and it made sense.

Originally Posted by stagstalker

What this man said ^ @JT_NZ

I read that article and just thought wow, that was one way of making what is a simple process a whole lot longer and more complicated and not even necessarily correct after all that!

If adjusting BC to true was a thing then people like Todd Hodnett and snipers all over the world would do it, buuut, they don’t.

Simple answer is buy a kestrel 2700 for out to 875y and when you want to play in the big kids sandpit get a 5700 and watch all the vids or come shoot with us with a heap of beer and sea food and we can get ya worked out!

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Tentman. Use what you have it. It will work fine. As long as you are within 0.2mil 300m>700m for this weekend you will fine. We can adjust your data if needed as we go. Most of what has been posted above is not really relevant to you for this weekends match.

Originally Posted by blair993

Tentman. Use what you have it. It will work fine. As long as you are within 0.2mil 300m>700m for this weekend you will fine. We can adjust your data if needed as we go. Most of what has been posted above is not really relevant to you for this weekends match.

And after that my offer still stands.

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Hey thanks guys, appreciated. I'm in a learning phase hence all the questions. Not worried and raring to try new stuff. We all gotta break-out of our comfort zones from time to time and the forum is a great resource to "jump" from!!

Originally Posted by andyanimal31

And after that my offer still stands.

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You always make it sound like your wasting your time and money unless you buy a nightforce scope and kestrel elite straight away and you wont get hits on target unless you do. Its not the only way to skin this cat.
The snipers hide math formula it not for making you dope card but to get you on target with NO info other than caliber. They use it to get students on target at courses rather than having to run them all over a crono and work out bc's etc. they are getting real world data on target not using a calculator then have to true it. And yes you should be truing your AB calc too.