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BC variance

I hope I'm posting this in the right forum. I am experiencing an interesting phenomenon. I am shooting B&N Sport Baracuda Hunter Extreme .25s out of an FX Wildcat MKI. I entered a BC of 0.0350 into Chairgun as is listed in the drop-down menu. My field testing of Chairgun's numbers is spot-on out to 75 yds. Then, the hold-overs necessary out to 100 yards from 75 yds start to be more than what Chairgun says. I shot out to 100 yds to see what the actual HO was. It was 3.00 mil-dots. Chairgun says it should be 2.68.

My hypothesis is that the BC holds valid out to 75 yds and then degrades for the remaining 25 yds out to 100 yds. After all, the BC is merely an average; it is variable as a function of many factors, including distance. What I did to test the hypothesis was interpolate the last 25 yds on a linear basis using the two known valid hold-offs at 75 and 100 yards as limits. (I know the function is parabolic; but I figure for such a short piece of the trajectory, linear is fine for a first approximation.) Now, at this point, I shot only one shot @ 88 yds using the interpolated HO of 2.17. (Chairgun says it should be 1.96.) She shot dead-on! So, I guess my reasoning is now a theory! (barely). I plan to go out to the range tomorrow and do a full test of my numbers.

Does anyone out there have any experience with this dynamic? Does my theory make sense from a physics standpoint?
 
Fair question, critta. I should have mentioned that I use a tilt technology range-finder. Therefore. the distance I am using against my Chairgun range card is always the horizontal distance, not the true distance, which changes as a function of the terrain inclination/declination. Good idea, though. It's interesting that you brought up this point. The reason I now use a tilt technology range-finder is precisely because I was having POI issues vis-a-vis my Chairgun numbers. I didn't notice the tilt issue until I got out in the field, because I was ranging at a formal range, which was a level field. It wasn't until I did some research that I discovered that the numbers on a range card are based on the horizontal distance. If you are not using a tilt technology range-finder, you must do an extra calculation to account for the elevation variations in the terrain. Thank you for your reply :). That would have been a simple fix if I was using a range-finder that returned only the true distance. (In fact, "true distance" should be considered a deceptive advertising term with regard to range-finders, because it sounds like a good thing, when actually it is a bad thing if the range-finder is used for hunting.