One of the neatest little free items available on the Internet is the simple ballistics calculator provided by Jackson Rifles based on work by Professor Arthur Pejsa. Just download the file pejsa ballistics.xls and open it and it’s ready to use. Everything else I’ve seen so far have been software programs that are computer operating system specific, i.e. they only work on the Microsoft Windows operating system. The Jackson-Pejsa ballistics calculator is a modified spreadsheet provided for download in Microsoft Office .xls format. However, for those of us who don’t use Microsoft Office the file is easily converted to the ISO standard Open Document format that can be used with the free and multi-platform Open Office or Libre Office.
To use the Pejsa-Jackson ballistics calculator first open it using your favorite spreadsheet program. In my screenshots I’m using OpenOffice on a Debian Linux system. Then use the “File – Save As” command to save it with a new name. I like to name the new file according to the bullet and loading I’m using so, for example, if I’m working with a 375H&H load using the Barnes 235gn TSX-FB bullet with a chronographed muzzle velocity of 3062fps I’ll call the new file something like “375H&H_Barnes_235gnTSX-FB_3062fps”. Once the file is saved with a new name you only have to enter in the new values in the first column replacing the sample values that are there in the original. Compare the changes I’ve made in the picture below with the picture at the head of this article.
As you can see in the first column which is labelled “Input Data” I’ve entered a new name for the Bullet Description, 3062 in the Muzzle Speed (fps) cell, 235 in Bullet wt (gn), 0.270 in BC (i.e. Ballistic Coefficient – figure from Barnes web site), 25 in Increment (yd) to get a 25 yard interval for my results, 300 in at Zero range (for a 300 yard zero in this case), and 1.8 for scope height as that is the height from the center of the bore to the center of my rifle-scope. Then click in an empty cell anywhere you like and the results will calculate (they’ll actually change as you enter each figure but ignore the figures until you’ve entered the final one.
You can then read your results by looking at the Range and Path columns. You can also click the “Gunstock Table” tab at the bottom of the spreadsheet to see the prepared trajectory table you could print and paste onto your gun-stock if you would like.
You can use this Ballistics Calculator on any computer you have that can open Microsoft Office documents. I have it on my Android tablet and I open it with the free WPS Office (i.e. Kingsoft Office). So if you do that you can just take your tablet and your chronograph out to the range and you’re all set to go.
A secondary use that might come in handy is for all you overworked and under paid school teachers out there who have been looking for a way to make math and spreadsheets interesting and relevant to your students. This spreadsheet and the math involved in it, along with a field trip to a rifle range and some hands on shooting would be a superb way to get high school students involved in spreadsheets and math – you might even be able to sneak in some trigonometry whilst you’re at it. Education should be relevant and fun shouldn’t it?
The Pejsa-Jackson Ballistic Calculator is one of those little known but fabulously useful free gifts. I’m sure you’ll get a lot of use out of it.
(Note: If you find the print in the pictures a bit small to read you can right click on the picture and choose the “View Image” option, then you can zoom it to see the detail. Alternatively you can right click on the picture and choose “Save Image As” and save each one so you can open them in a picture viewer and see them more clearly.)