BC vs CD and calculating each from LabRadar Velosity tables

[PerkyVal]

OK, so now I got my LabRadar and decided to use Ballistic Coefficient as a means to finding the right speed for a given projectile at a given range. The LabRadar gives me all the velocity data I need but it doesn't calculate the BC at any given distance.

So, being the clever girl I am, I went searching for a excel formula, or spreadsheet that would do this for me. What I found is making my head hurt (yeah, I'm a blonde).

Apparently there is something called a Drag Coefficient (CD) which maybe more accurate than the BC, and is what militaries use.This is not the Drag Law (G1, G2...etc) that we enter into our favorite airgun ballistic programs.

So, I'm guessing someone smarter than me has developed a spreadsheet, or database program that would do both from the data imported from a excel .csv file that I get with LabRadar. Failing that, perhaps someone has the formulas formatted so I can drop them into a Excel spreadsheet.

I'm thinking that "Yrrah" has done this, but it looks like he hasn't been around in a while.

Any ideas?

 

[PelletPusher]

Paging @Yrrah

 

[txrpls]

Not a formula, but Chairgun has a tool that does the computations.

 

[SMH77]

Use Chairgun and input the velocities at the different distances along with the environmental data. Probably want to use the GA profile for the diabolo pellet shape. You will notice the BC changes when you enter the velocities using different distance pairs. I've settled on using velocity at 1 yard and at 50 yards for all my BC comparison work since 50 yards is pretty typical airgun range, and 1 yard allows enough time for the exit dynamics to mostly settle down (I'm using two chronographs). Using this method has worked pretty well to create DOPE cards for different distances that seem to be fairly spot on at distances out to 125 yards. The same DOPE cards can be made by shooting groups at varying distances and recording what compensation was needed at each distance-that's the 'real' way to get it accurate.

You'll likely end up with a bunch of questions when you start recording / calculating BC's from the velocity data. Yrrah has a lot of historical posts that delve pretty deep into the topics (including some of the stuff I've referenced in my previous paragraph). Enjoy the learning curve and congrats on the LabRadar.



Sean

 

[JungleShooter]

For spreadsheets and BC calculations, besides Yrrah there is Bob Sterne, aka rsterne, usually very active on the GTA forum:

https://www.gatewaytoairguns.org

He researches and posts so much they gave him his own sub-forum:

https://www.gatewaytoairguns.org/GTA/index.php?board=224.0

I remember him writing about having prepared some spreadsheets, and he anticipates doing extensive work with a Labradar in a couple of years when he's got more time.

 

[Yrrah]

ATTENTION Perky Val: I would like to help but unfortunately my old tower computer has a lot of problems and the operating program, relevant to what you are asking for, is presently lost in there somewhere.

Dave Eades (Harry's Lad) wrote this programme specifically for me when I acquired the Labradar. I had earlier given Dave data shot over chronographs to 200 yd, showing how bc changes with range/time with our diablo pellets, to assist him in evolving the GA for his Chairgun which he passed on to Hawke.

I think the following pic shows what you are asking about. The 4th last column is range out to 19+ yd; 3rd last column is drag coefficient Cd; then bc using from memory G1; the last in bc using GA for diabolos (but generically derived from the data I suplied for .25 Kings).

This sample is for one shot with 8.44 gr .177 JSB Exacts. Note that had the data extended to longer range, when dynamic stability and yaw had settled, bc and Cd may well have shown positive change. You should be able to expand the pic to view if necessary. ....

If you can contact Dave and tell him I referred you on, then he may be able to re-locate the programme. It is some years now since he and I were in touch and I am not sure of his present situation. He had re-located to Spain from UK.

Kind regards, Harry Fuller (Yrrah in OZ).