best Ballistic Coefficient calculator

[GSPV]

Geez guys, give the OP a break. He wants to tweak the BC for some reason. Why not just trust the guy? Maybe he is using bullets that he doesn’t have good published BC for. Maybe he makes his own bullets. Maybe he points his bullets. Maybe he just likes doing it.

The bottom line is that with known velocity and change in velocity and/or observed drop, he can back into the BC with virtually any app.

 

[STOMP442]

I got a top 10 finish at the ELR match in Wyoming last week so I think I'm good.

Proud of ya.

Wow, proof by eminent authority? MIT teaches that the method is no proof at all.

1. Proof by reference to eminent authority: “I saw Fermat in the elevator and he said he had a proof . . .”

I'll take reliable empirical data every time - though I majored in theoretical math, I concur with the view that facts are stubborn things.

What exactly did I say that was wrong here? Are you Saying the testing and results achieved by Litz and Applied Ballistics are wrong? Pretty sure most folks would agree that he is probably the best resource of ballistics data available. Why not use it?

 

[dellet]

Is there a reason you can not use a regular math formula app by creating and saving the formulas for calculating BC by both velocity and distance drops?

 

[GSPV]

Is there a reason you can not use a regular math formula app by creating and saving the formulas for calculating BC by both velocity and distance drops?

I’m not the OP, but I’ve never been able to get past the “coefficient of form” variable in the BC formula. YMMV.

 

[spife7980]

I’m not the OP, but I’ve never been able to get past the “coefficient of form” variable in the BC formula. YMMV.

I get it in that the Sectional Density/G7=Form Factor and I understand that the better BC for its weight vs just a heavier bullet with a corresponding BC. Thats all summed up nicely in plenty of articles.

But if we are trying to develop a BC from scratch then we dont have the g7 to divide by as its what we are discovering, we have 2 unknowns, BC & FF.
Its the initial development of that FF number that stumps me. Well, its the mathematical derivation that stumps me. I get that you could actually shoot it at distance, true up the BC in your calculator and then being able to divide by the SD and back into the FF. I want to know how its developed without taking the short cut of shooting it.

But I guess that involves figuring out a bullets individual drag coefficient which is a whole other bag of worms.

 

[GSPV]

Exactly. And you’d end up shooting it anyway to test your calculations.

My thought is for the OP to shoot, gather velocity and drops and then twiddle with the BC until the predicted trajectory and downrange velocity matches his observed trajectory and downrange velocity.

At that point, the BC would do what it is supposed to do...predict trajectory.

 

[pouriya]

i found the JBM online calculation but it is only online and very accurate! any one knows any app that can do this?

 

[mensajd]

The Ballistic: AE app uses the JBM ballistics engine. I don't care for the app's UI/UX however.

 

[Ray B]

About 20 years ago either Handloader or Rifle magazine had an article on how to compute BC when you know the two velocities of a bullet and the distance between the bullet's velocity measuring points. For example, 2700 fps @ 15', 2550 fps @ 315'; decrease 150 fps in 300'. It was a fairly simple calculation, all I need to do now is find that copy of the magazine.

 

[JohnKielly]

About 20 years ago either Handloader or Rifle magazine had an article on how to compute BC when you know the two velocities of a bullet and the distance between the bullet's velocity measuring points.

Damn, and I thought that I was cool having one chronograph.

 

[GSPV]

The LabRadar chrony can measure down-range velocity.

 

[Ray B]

Damn, and I thought that I was cool having one chronograph.

Using a Chrony I didn't even try to put bullets through the target opening at any distances beyond 10 yards, let alone 100 yards. So I was not able to get the data on handloaded bullets to compare the calculated BC with the advertised BC. The main use I found for the formula was using factory ballistic chards such as supplied by Winchester and Remington to calculate the BC of the several factory ammunition bullets.

 

[bigngreen]

Is that so? With ease?

Damn near every calculator will get you to 1k without issue. Why is it that I had to adjust my BC .020+/- on a Berger 180 Hybrid to get it anywhere near what AB was telling me. If you want to drink the Koolaide please enjoy it, but there are reasons for adjusting the BC. I actually thought AB would allow me to adjust BC to match actual drop, but it only allows you to adjust velocity to match your dope. If I tried to adjust velocity in AB to match what I was shooting at ELR ranges, the output turned to garbage. I even bought the "Custom Curve" for the bullet from AB, even worse data. The only thing that would work was manually adjusting BC to match my dope.

Did you not find the ballistic calibration in app, range 1 is for fine tuning speed and range 2 & 3 tune the drag. Works quite well.

 

[GSPV]

Using a Chrony I didn't even try to put bullets through the target opening at any distances beyond 10 yards, let alone 100 yards. So I was not able to get the data on handloaded bullets to compare the calculated BC with the advertised BC. The main use I found for the formula was using factory ballistic chards such as supplied by Winchester and Remington to calculate the BC of the several factory ammunition bullets.

You can also back into the observed BC with drop data. Better to have velocity *and* drop, but you can do it with drop. Use JBM or similar, plug in the values that you know and play with the BC until you get a predicted trajectory that matches your actual.

 

[Delfuego]

Did you not find the ballistic calibration in app, range 1 is for fine tuning speed and range 2 & 3 tune the drag. Works quite well.

That calibration only adjusts the velocity, not the BC.

 

[bigngreen]

It tunes your velocity on step one, steps two and three tune your drag, it's in the user manual and I use it all the time even to tune up a custom drag curve.

 

[Delfuego]

It tunes your velocity on step one, steps two and three tune your drag, it's in the user manual and I use it all the time even to tune up a custom drag curve.

Either way. It did not work for me. The output was garbage. I attempted to "true" at multiple distances out to 1660 yards. I used different combinations of distances and got lots of different answers, none of which would match actual dope, some were fantastically wrong.

In the end, manually adjusting the BC and using the actual velocity proved most accurate out to 2000 yards.