# Ballistics for Excel Forum

## BfX => Ballistic coeficients => Topic started by: mman on November 02, 2011, 09:40:47 PM

Title: 22 LR bc
Post by: mman on November 02, 2011, 09:40:47 PM
Update: My modified CED M2 chrono is now ready and I made a quick BC test with lapua midas+ 22 lr. ammo between 3,5 and 144,5 meters.

Gun is Sako P94 varmint, ammo lot is 06843/51325 and atmospheric conditions during the test were: +5 C, 997 hPa, 95%.

Here are the results:

String  V3,5

1)   323.1
2)   321.9
3)   321.9

High:    323.1
Low:    321.9
E.S.:      1.2
Ave.:    322.3
S.D.:      0.6

String V144,5

1)   262.0
2)   257.8
3)   255.2
4)   260.0
5)   258.0

High:    262.0
Low:    255.2
E.S.:      6.8
Ave.:    258.6
S.D.:      2.3

By using these as input values one can calculate that BC is:

RA4 bc = 0,113 (with JBM)
RA4 bc = 0,110 (with BFX)

I think that difference between these values is due to two things. For some reason RA4 drag curves are not exactly the same in these two calculators and there is some minor differences in air density models. My personal estimate is that accuracy of this BC test is about +/- 5%. Consequently results are in line with those presented in McCoy's .22 lr bullet study which suggests 0,113 RA4 BC for tenex round nose when using BFX as a ballistic solver.

Title: Re: 22 LR bc
Post by: admin on November 03, 2011, 10:03:26 PM
These are things I like :D By the way you can now use a custom drag table (e.g. the jbm one).

I get a bit different results. I think there are two variables here: the average v0 and the average bc. I have, using solver, optimized them both to get a best fit with the data.

bc   0,108   ra4
v0   324,6   m/s

I have included the spreadsheet that does the job. The spreadsheet can be used to determine the accuracy of the fitted values - i did not do it.

mman, are you having ICAO conditions for the measurements or is the weather in Finland a bit ::) colder?
Title: Re: 22 LR bc
Post by: mman on November 04, 2011, 07:26:52 AM
mman, are you having ICAO conditions for the measurements or is the weather in Finland a bit ::) colder?

atmospheric conditions during the test were: +5 C, 997 hPa, 95%.

I think this is the reason why we got different results. You should use test conditions instead of ICAO when calculating BC value.

Thanks for the spreadsheet, I'll add features to change BC format and atmospheric conditions and will use it next time when measuring BCs.
Title: Re: 22 LR bc
Post by: admin on November 04, 2011, 02:05:21 PM