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#181
##### Ballistics / For which atmospheric conditions did Pejsa derive his drag functions
February 17, 2011, 12:46:44 AM
Delved deep in the issue, Pejsa was not clear about it. However on page 76 in his book he stated that he adjusted his A function to equal the Mayevski a function at 2600fps.

this means that he uses the Ingalls conditions P=30inchHg, T=60F, humidity=67%.

The (ICAO air density)/(Ingals air density)=1.00371. Although the effects will be minor to the point of being neglible, I will adapt Pejsa's drag calculations in BfX to ICAO. Furthermore, I will add Mayevski Ingalls (under ICAO conditions) drag functions.

#182
##### Ballistics / Quick comparision to Lapuas radar measurements and Lapua's QuickTarget
February 15, 2011, 09:01:48 AM
Lapua has radar measurements for many of its bullets. From this their specific drag functions has been calculated. I downloaded the free Lapua QuickTarget ballistic calculator from www.lapua.com and made a quick comparision of its output for the Lapua GB478 Scenar 6,8 gram (105 gr) 6mm NormaBR bullet. Later, after I have sorted out things with Pejsa's calculations (did he use US Army Standard Metro or ICAO conditions plus 78% humidity?) I will do a more elaborate calculation. I think the results are pretty good. The question is how well the QuickTarget calculations match the exact trajectory? Ideally one wants to compare calculations with the actual path properties too!
#183
##### Member projects / Re: Ballistics Displayed My Way
February 14, 2011, 02:13:01 PM
it works with my excel2007 on a 32 bit machine:
#184
##### Member projects / Re: Ballistics Displayed My Way
February 14, 2011, 01:42:23 PM
can you show me your =bfx_help(1)?

#185
##### Member projects / Re: Ballistics Displayed My Way
February 14, 2011, 10:43:15 AM
yes, bfx_u allows that the user can specify his/her own units for in and output. This is not only handy for the metric/imperial units, but also if MoA or a distance is desired.
#186
##### Member projects / Re: Ballistics Displayed My Way
February 13, 2011, 10:29:01 AM
Nice!

have look at =bfx_u(output_unit, value, input_unit)
#187
##### Updates / Re: BFX update - BfX_C bug fixed
February 11, 2011, 06:04:17 PM
... delving deeper in the book of Pejsa, he has used Ingalls, Us Standard Metro and ICAO data / tables. Which one he used to compute the (de)acceleration has to be reverse engineered...
#188
##### Updates / BFX update - BfX_C bug fixed
February 11, 2011, 01:29:48 AM
BfX_C works as it should!
#189
##### General discussion / Re: BfX atmospheric conditions
February 11, 2011, 01:28:39 AM
Bug in BfX_C is fixed
#190
##### General discussion / BfX atmospheric conditions
February 11, 2011, 12:37:34 AM
Dear all,
Lately I was confused which atmospheric conditions I used in BfX - it was too long ago to remember and it seemed I also forgot the physics behind the drag functions.

Okay. Drag functions are independend of atmospheric conditions.

In the calculation of drag you have to use a density of air. In BfX the ICAO conditions are used (15 degrees C and 101324,6 Pascal 0% humidity), which are common for present day ballistic programs. Just checked the code - I am sure again - it holds for any BfX drag function

There is also the US Army standard meteo conditions (15 degrees C and 99991,6 Pascal), frequently used in the past. BFX_C which is used to convert ballistic coefficients, contains a bug thatI will soon fix. It incorrectly converts the ballistic coeficient as it assumes that BfX uses the US Army standard meteo conditions. if you enter
=BfX_C() and you  see the output BfX_C(T=15 [Celcius]; P=99999.76 [Pascal] []) then this is erronuous.

The new version will show BfX_C(T=15 [Celcius]; P=101324,6 [Pascal])

Expect the correction soon.

#191
##### Updates / small update of BfX
January 22, 2011, 10:03:50 PM
I have added, inspired by a posting of jrmy_1, the iphy (inch per hundred yards) and cphm (cm per hundred meter) units of angle  iphy=tan(angle)*100*0,9144/2,54) and cphm=10000*tan(angle)

e.g. =bfx_u("iphy";1;"moa")

to install the update you can use the setup or simply replace the .xll file
#192
##### Member projects / Re: Developing Long Range G7 Spreadsheet
January 17, 2011, 10:12:00 PM
by the way, one of the most commonly ignored issue to achieve a one shot one kill setup is the calibration of the sights. Is the scope according to the specs?

I have a scope - 230 euros - that has a reasonable optical quality, and has an excelent mechanical quality. I see the black dot in the sight and that is good enough for me. Anyhow, the optical quality was good enough to become 1st in the Dutch 2008 300-500-600 yards (yes yards in the Netherlands too!) F-Class championship and third in 2009. In 2010 the beautiful military shooting range was (probably temporary) closed for us  .  Mechanically the scope is very constant in its moa/click and has no hysterises I know of. But instead of being 1/4 moa per click it is 0,21 or so. And that is an issue if you have to depend on calculations (the rifle was zeroed at 100m and I shot a lot at 500m).

I have a workbook illustrating a scope calibration.
#193
##### Member projects / Re: Developing Long Range G7 Spreadsheet
January 17, 2011, 09:44:39 AM
regarding humidity, I did not capture its effects in BfX_C.
#194
##### Member projects / Re: Developing Long Range G7 Spreadsheet
January 17, 2011, 08:40:45 AM
Welcome, in principle you want a fire control system for a hunting rifle. For target shooters BfX does the job, mostly because the elevations are never in excess of 15 degrees and we are allowed to sight in.
In some  hunting situations (which do not exist in our almost flat Netherlands) you have to shoot up/downhill and the elevations are such that BfX becomes too inaccurate. Furthermore BfX does indeed not include the effects of spin drift and the Coriolis force. They would complicate the BfX-interface and I found  their practical influence, compared to those of wind, negligible. I you would, you can add some formulas to Excel and compute their effect. To release software which has all the capabilities you mention is entirely possible, but I will not do that. There are people who shoot something else than paper targets, use other launchers then rifles and who aim at our soldiers in the mountains of Afganistan.

The last time I checked I found that Excel on Windows mobile does not support add-ins. In my experience the use of tables printed on paper (covered with plastic if you like) is much easier than the use of electronic devices during matches.  I simply do not have the ability to think when there is time pressure.

In the spreadsheet GettingStarted with Excel you will learn everything about generating such tables, including the effects of temperature and pressure. I am not sure if I have still included the effects of humidity, since they are so small for rifle bullets. It will also educate on the use of G1 versus G7 drag functions.