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All Springer/NP/PCP Air Gun Discussion General > "Bob and Lloyds Workshop"

Cast Bullet Database - A Work In Progress

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rsterne:
I have had a request to make up a chart on my new version of Bob's Boattails, with the specifications such as weight, length, SD and Twist.... I included a couple of Flat Base offspring as well.... Obviously only a small number of these are available, but it shows what could be made, if the desire is there.... I built it in Excel, but the Forum would not let me attach that, so I had to rearrange it and print it as a .pdf file.... It is attached below.... If you have any questions, please post them in this thread....

Bob

Back_Roads:
 In general nice layout, makes it easy to see if any of my hairbrain ideas have a glimmer of hope, and also confirmation as why things I tried do work.
 Thanks for the cookies Bob :)

rsterne:
I have updated the Database in the first post to Version 11.... I am still using G1 for the BC's because that is the most popular, however, for most airgun slugs, using the RA4 drag model.... along with the BC(RA4) of course.... will give more accurate trajectories....

Bob

rsterne:
I have updated the Database in the first post to Version 12.... Ballistic Coefficients for many .257 and .224 cal slugs have been added.... I am still using the G1 drag model because is is the most commonly used, but in every slug I test now, the RA4 drag model is a better "fit".... The BC changes less over a wider range of velocities using RA4 instead of G1.... Fortunately, there is an easy to use converter you can find here.... https://www.jbmballistics.com/cgi-bin/jbmgf-5.1.cgi

Input the "BC" from my Database, selecting "G1" for the input.... Input the "Calibre" and "Bulet Weight", and the "Velocity", and then select "RA4" as the "New Drag Function".... When you hit "Calculate" you will see a table, and the left lower number is the one you want, the "New Ballistic Coefficient: 0.XXX RA4".... Use that in your Ballistics Calculator after selecting RA4 as the drag model....

Bob

rsterne:
I realized that I was using the average velocity as measured at the site conditions in the "Avg. Vel." column.... The BC is corrected to ICAO standard atmospheric conditions, and the velocity should have been as well.... I have gone back over all my data and made this change to the Database.... and yes, it was a LOT of work.... The previously stated velocity for most of the data has decreased about 15-20 fps, and the column is now labelled "ICAO Vel.".... The BC stated now corresponds to that velocity, as it should, from Version 13 onwards.... This change should allow a more accurate conversion from G1 to other drag models, such as RA4....

Sorry for the ongoing small error, but you won't need to worry about it in future, as I have updated my spreadsheet to report the ICAO velocity, along with the BC....

Bob

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