How To Use Ballistic_XLR: Extended Data
Extended data is meant to be used to interpolate and for direct results. The table consists of windage and elevation settings for increases in barometric pressure and wind speed. Wind drift data is keyed for varied wind speed speeds of 5mph, 10mph, 15mph, 20mph, 30mph at specific barometric pressures. The pressure variances are in increments of 1 inch of mercury (about 34Hpa) and go up and down from your station pressure for 3 intervals each. So if you list 27inHg as your station pressure on the Pocket PC Input page then you will have both wind and drop data for 24, 25, 26 and 28, 29, 30inHg on the Extended Data tab.
Now let’s cover a use case. You’re out in the field doing some extreme long range precision training. You’ve set your chart for nominal barometric pressure of 27.5inHg and your area of operations tends to languish around that value and it’s been hanging there just fine for 2 days. Your target is set up and you’ve spent the day clanging steel with good success. You wake the next day to find that the weather has taken a serious turn and you pull out your Kestrel and find that the barometric pressure has dropped to 26.7inHg. You know that this is going to affect your DOPE and you’re running low on ammo and you want to get some shots on video for a little bragging rights. How to solve the conundrum. Easy.
Your target is at 1050m which means even a couple clicks off and you’ll have a wasted shot. You pull out your Extended Data table and look up the drops at the nearest 100yrd/m intervals to where your target is. In this case you find the drop for the temperature and pressure you’re at at 1000m and at 1100m. We’ll call this 8.62MRAD and 10.23MRAD. Almost 2MRAD betwen those two points is a LOT of difference. Now go back to your Table 10 data (it’s important to use Table 10 if at all possible) and get the indicated drop at station pressure and at the temp you’re at as well as the indicated drop for 1000m and 1100m. We’ll call this 9.62, 8.81 and 10.48 respectively. Now we see that at 1000m the difference of 1inHg meant .2MRAD at 1000m and .25MRAD at 1100m. So we see the difference is .2MRAD on average and we pull .2MRAD out of our elevation calculation.
From this we see that localized interpolation can be very flexible and provide useful and accurate data. The key of this is to find your indicated data from your station pressure tables and then to find the differences between comparable points on the trajectory that are nearby and at 100m/yrds brackets. Note that at 1050m .2MRAD at 1050m is just about 8 inches. That’s the difference between a hit and a miss and it’s the reason that Ballistic_XLR is stuffed full of points of interpolation meant to get you within about .5MOA or .2MRAD (2 clicks) of your target even when conditions change.
The way we did the barometric pressure also applies to the windage. Windage changes at long range due to barometric pressure changes can easily be not insignificant. As well differences in wind speed dramatically affect trajectory and need to be carefully doped. A 10mph wind can easily put in 3x as much drift as a 5mph wind and things get really dramatic after 15mph. Interpolation is done the same way. Find the difference between your bracketed 100m intervals and then find the data for your actual range and apply that difference.