What drag function does Chairgun use?

What drag function does Chairgun use?

Joined: January 22nd, 2007, 10:28 pm

April 10th, 2012, 8:56 pm #1

And, are there conversions for G1 or GL etc?

I really like the Chairgun program and the feature set is fantastic. However, I'm not convinced that the BC calculation is the best fit for big bore projectiles.

The BC figures I get using Chairgun differ from any other ballistic calculator I use, regardless of the drag function selected (except for Steve's at airgunexpo but then, that IS the Chairgun computation, right?)

Has the Chairgun BC calculation been optimized for the diablo form? Does it even matter? I suppose if Chairgun uses a unique drag function, the subsequent calculations may all remain valid if the math remains consistent. I'm not smart enough to know but since I've found very significant deltas between BC calculated at high velocities vs. low velocity with the same bullets, I don't know how valid the results (trajectory tables) Chairgun produces are...for my application. (I've seen that some have made remarkably accurate scope tapes using Chairgun.)

BTW, I have done a little bit of testing a while back but I only used the output to get me on paper, I didn't gather enough data to verify anything. Now, I'm trying to develope some scope tables and optimize a set-up so that I can get the most out of my next range opportunity.

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Joined: August 6th, 2010, 11:56 pm

April 11th, 2012, 12:04 am #2

I may not be able to explain this elegantly or correctly for that matter but it shouldn't matter what AIR GUN PROJECTILE you are using just as long as you input the correct ballistic coefficient and of course the other corresponding information that's needed. Steve in NC would be the person to correctly answer this question.

-Keoni

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Joined: January 22nd, 2007, 10:28 pm

April 11th, 2012, 9:10 pm #3

" as long as you input the correct ballistic coefficient"
The correct ballistic coefficient is computed by using the correct drag function.

Drag functions vary according to projectile shape and also can be divided into velocity "zones" for more accurate ballistic predictions. Some manufacturers provide more than one BC for up to 3 velocity zones so ballistic software capable of using multiple BCs can predict a more accurate path.

Since Chairgun does not have a selection to account for projectile shape or drag function, it is using a custom drag function equivelent. I was hoping that conversion factors for projectiles other than diablos might might be available such that the program might be a better tool for big bore shooters.

Naturally, I can go shoot and fine tune the BC until the Chairgun graph matches my data for a certain set of ranges but what's the point in that? I'm trying to predict performance and then fine tune at the range.
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Joined: August 6th, 2010, 11:56 pm

April 11th, 2012, 11:06 pm #4

Just using your chrony and getting a reading from the near distance (1 yard) and one at the far distance (the distance you are normally shooting to) and do the math (just use Chairgun) and it will calculate the BC. Of course if you are using different projectiles you will have different BC values.

-Keoni

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<table width="600" border="0" cellspacing="1" cellpadding="0"><tr><td width="33" height="33"></td><td><font size="3">Download Airgun Helper Mobile for Android 2.2+ smart phones</font></td></tr></table>
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Joined: January 22nd, 2007, 10:28 pm

April 12th, 2012, 1:33 pm #5

I think you've missed my point. I've already gathered the near far velocities and ambient conditions. Every other ballistic calculator outputs a BC different from Chairgun, regardless of the drag function used. Unlike other ballistic calculators, Chairgun does not provide for selecting drag functions, so obviously, it uses the same calculations for every projectile. The output shoes that those calculations do not use any of the common drag functions.
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