Are Ballistic Coefficients Still Relevant?

[NateChrony]

G1 is useless for airgun pellets and slugs. I believe I read from ballistic boy that the correct one is GA and RA1 for boat tail slugs.

spot on... you need the correct REFERENCE PROJECTILE... and with the massive amount of advances in projectiles in AirGuns - they just dont exist, thats the problem.

I know BallisticBoy & have had many discussions when I started to hit the wall trying to find out a BC number. I believe he used to work for governments in artillery testing, he's had access to the most expensive kit on the planet. I trust his knowledge.

 

[NateChrony]

Have a look for the paper by Nicos Ladommatos - "Drag coefficients of air rifle pellets with wide range of geometries" - i find it absolutely incredible & something I would never have thought.

https://www.researchgate.net/publication/350733983_Drag_coefficients_of_air_rifle_pellets_with_wide_range_of_geometries

There's another paper "influence of air rifle pellet geometry on aerodynamic drag" from Nicos too.

Here's an example of tiny differences making a huge difference to drag


So how many reference projectiles do we need?

 

[Madhatter]

I'm not sure if this link will work.

Search results for query: Ballisticboy

www.airgunnation.com

 

[NateChrony]

The only thing I could find (I could be wrong - again, produce the formula to prove me wrong) that provides a "air resistance efficiency number" type of thing is the Coefficient of Drag - Cd


That can be calculated directly from the 2 speeds & air density, HOWEVER is only a number for the specific velocity.
I'd say the 2 relevant numbers for Air gunners would be:
- Cd at 12fpe - a very common power level, good for .177's
- Cd at the highest power level for that projectile that shows accuracy/stability. Maybe 900fps by default?

 

[NateChrony]

So, how do you use your numbers in Chairgun Elite, or any Ballistic Calculator, without a BC number when shooting pigeons or rats at various distances? Like I said, just trying to learn more.

Superb question - and half the problem! They're supporting/pushing something which isnt 100% accurate.
It seems a left over from the powder burners - artillery moved on decades ago, they keep pushing it - possibly because they have a "limited" selection of projectile forms?

You can use a few online calculators to "get a number" that will be close-ish, depending on how close your projectile is to the reference.

Matt does a YouTube video "What Everyone Gets Wrong about Ballistic Coefficients (Boat Tail Slug DEEP DIVE)", does explain it well at 20:21, but then goes on to spend ages fudging numbers in spreadsheets to "get a number". Not sure what this achieves.

 

[Solo1]

Superb question - and half the problem! They're supporting/pushing something which isnt 100% accurate.
It seems a left over from the powder burners - artillery moved on decades ago, they keep pushing it - possibly because they have a "limited" selection of projectile forms?

You can use a few online calculators to "get a number" that will be close-ish, depending on how close your projectile is to the reference.

Matt does a YouTube video "What Everyone Gets Wrong about Ballistic Coefficients (Boat Tail Slug DEEP DIVE)", does explain it well at 20:21, but then goes on to spend ages fudging numbers in spreadsheets to "get a number". Not sure what this achieves.

Well obviously he’s looking for a number he can plug into his software to give him a number of clicks on his scope to answer for distance thats what its all about

 

[Billm]

I only have one question: are Miles and Ballistic Boy the same person? Personally, I don’t pay attention to published BC numbers. I shoot a number of projectiles over the chronograph and get a solid average and I do it again at 100yds. I then use the calculator to give me a rough BC. Then I shoot it at the proscribed drop for 100yds and adjust the bc until it matches the real world drop. It works for my humble shooting and so who cares if it’s not correct textbook science. I know a lot of shooters do the same. I find manufacturers numbers to be more of a marketing thing and I treat it as such. I suspect this discussion is more about whether the FX Chronograph calculates a useful BC. I don’t know, I wish I could try one.

 

[NateChrony]

Well obviously he’s looking for a number he can plug into his software to give him a number of clicks on his scope to answer for distance thats what its all about

That was my point - if the scope manufacturers asked for a velocity & Cd (& environmentals) - it would be perfect every time without any extra work.

 

[NateChrony]

I shoot a number of projectiles over the chronograph and get a solid average and I do it again at 100yds. I then use the calculator to give me a rough BC. Then I shoot it at the proscribed drop for 100yds and adjust the bc until it matches the real world drop. It works for my humble shooting and so who cares if it’s textbook science.

This will work - but only (ish) for a single velocity & single distance. The BC provides performance at different velocities.

What this does in practice is to take 2 different curves & make them match at a specific velocity - so you'll get the right drops at that velocity.
Depending on how close your "actual" curve is to the one chosen -
- lower/higher initial velocities will vary potentially significantly
- over shorter/longer distances (more time in the slower speeds) drops may be different

 

[jps2486]

Not much I can do about it, so I ignore it.

 

[FL22]

Why do I feel like we are being lead down the path of a future product solution.

@NateChrony on with it, spill the beans .

 

[NateChrony]

Why do I feel like we are being lead down the path of a future product solution.

@NateChrony on with it, spill the beans .

nope - my products provide Cd numbers as its the only mathematically accurate thing to provide.

Doing my bit to help us move on from an outdated method & help people to understand what it actually is. There was a good little post from ZAN about it & why they dont provide BC.
I suspect this will become an increasingly larger problem for Airgunners as pellet/slug development continues, with increasingly larger numbers of different shaped projectiles.

 

[Non Timebo Mala]

G1 is useless for airgun pellets and slugs. I believe I read from ballistic boy that the correct one is GA and RA1 for boat tail slugs.

RA1 is for rim fire ammunition, specifically .22LR

 

[Non Timebo Mala]

nope - my products provide Cd numbers as its the only mathematically accurate thing to provide.

Doing my bit to help us move on from an outdated method & help people to understand what it actually is. There was a good little post from ZAN about it & why they dont provide BC.
I suspect this will become an increasingly larger problem for Airgunners as pellet/slug development continues, with increasingly larger numbers of different shaped projectiles.

I think you are mostly right.

Here is my take:

As you, no doubt, already know a ballistics model is just a curve used to describe the drag behavior of a projectile at various velocities. Why do we have it? Because computers have not always been with us. There was a time when the ballistics engineer started with a ballistics pendulum and a pencil and paper. He did all the math. Along came graphs and other methods of estimating the correct answer. If your target was the size of a ship and you didn't care where you hit it you were good.

That brings up the topic of accuracy. Accuracy isn't perfection. It is a sufficiency. It your projectile lands close enough to the aiming point to deliver the desired effect then accuracy is "good enough".

Sometimes people strive for perfection. Here is where the bench rest crowd raises their hands but even with them the goal is winning the match, not perfection, else they would just shoot at home against themselves in their quest for perfection.

BC exists because it is "good enough" for all but the most exacting endeavors.

All that said, even if you calculate with perfect accuracy, you will never measure with the same level of accuracy, so all this talk about "exactness" really is still relative, isn't it?

Your goal is admirable. Don't let it become an obsession.

 

[BBGunn]

I think you are mostly right.

Here is my take:

As you, no doubt, already know a ballistics model is just a curve used to describe the drag behavior of a projectile at various velocities. Why do we have it? Because computers have not always been with us. There was a time when the ballistics engineer started with a ballistics pendulum and a pencil and paper. He did all the math. Along came graphs and other methods of estimating the correct answer. If your target was the size of a ship and you didn't care where you hit it you were good.

That brings up the topic of accuracy. Accuracy isn't perfection. It is a sufficiency. It your projectile lands close enough to the aiming point to deliver the desired effect then accuracy is "good enough".

Sometimes people strive for perfection. Here is where the bench rest crowd raises their hands but even with them the goal is winning the match, not perfection, else they would just shoot at home against themselves in their quest for perfection.

BC exists because it is "good enough" for all but the most exacting endeavors.

All that said, even if you calculate with perfect accuracy, you will never measure with the same level of accuracy, so all this talk about "exactness" really is still relative, isn't it?

Your goal is admirable. Don't let it become an obsession.

That's pretty much they way I prioritize my own need for airgun projectile ballistics. I get what I need for my air rifle hunting by actually shooting my second zero, and my furthest distance that I limit myself to shooting at a particular animal. Then I 'tweak' the numbers in a basic ballistic program until the numbers all match. Of course it's not 'exact', but the process is so close that hit's in the vitals are assured.

Having written that..., I understand the need for some folks to pursue perfection in the arena of airgun ballistics, it's how our minds all work differently. So, to those pioneers in new airgun ballistics, please carry on as we all benefit in one way, or another.

 

[duchunter007]

Superb question - and half the problem! They're supporting/pushing something which isnt 100% accurate.
It seems a left over from the powder burners - artillery moved on decades ago, they keep pushing it - possibly because they have a "limited" selection of projectile forms?

You can use a few online calculators to "get a number" that will be close-ish, depending on how close your projectile is to the reference.

Matt does a YouTube video "What Everyone Gets Wrong about Ballistic Coefficients (Boat Tail Slug DEEP DIVE)", does explain it well at 20:21, but then goes on to spend ages fudging numbers in spreadsheets to "get a number". Not sure what this achieves.

Nate,

Thank you, I am trying to ask relevant questions
Matt's video is good, and I have watched it a couple of times.
How do you use "CD" numbers in figuring ballistic calculations?
I guess I will need to add another Chrono to my collection to get those "CD" numbers

Andrew

 

[Solo1]

Ya if cd numbers are better teach away!

 

[Madhatter]

RA1 is for rim fire ammunition, specifically .22LR

But it works for boat tail slugs. 22rf slugs are rebated tail slugs like most airgun BT slugs.

 

[NateChrony]

How do you use "CD" numbers in figuring ballistic calculations?
Andrew

The trick is a BC isnt a single number, its a drag curve, a collection of numbers: drag coefficients of at different speeds.

Using a Cd in ballistic calcs....

Depends on what you want to do...
If you want to find the "most efficient projectile" for you - a single Cd value at the initial speed you'll use your pellet at will give you that answer.

If you want to calculate drop of projectiles:
At a specified/single distance: a Cd value at that initial speed & distance will work.

If you want to calculate drop of projectiles at different distances:
You need a drag curve - as the projectile will potentially be moving through all the different velocities as it goes down range.


Is the BC relevant?
Its relevancy is going to decrease more & more, as it will potentially be less & less accurate as manufacturers innovate.

Is it good enough?
For some yes - absolutely 100%, if the projectile is close to the reference model - it will absolutely work.

The magic solution?
Manufacturers would provide drag curves, or 5(depends on the curve flatness) data points on their projectiles over the typical speeds its used at. You would then plug these into the ballistic calculator.


The #1 biggest issue with BC's is that they can be mis-used & leveraged for marketing, and used to mis-lead the consumer.

 

[NateChrony]

Sometimes people strive for perfection. Here is where the bench rest crowd raises their hands but even with them the goal is winning the match, not perfection, else they would just shoot at home against themselves in their quest for perfection.

BC exists because it is "good enough" for all but the most exacting endeavors.

Your goal is admirable. Don't let it become an obsession.

100% agree...
Dont worry - but be well aware the magical "BC" number may not be correct or useful & need additional work.

Obsession?
ha! i'm in the wrong game for that - my OCD is going nuts