Number one by a wide margin would be the adjustments of the scope.
This is what I'm thinking in hind sight because my 400 and 500 yard shots were very good using the B&C hash marks. Things went downhill when I started dialing. I didn't even think about that until the next day.
Number two would be the BC of the bullet, some of the LRAB's have been pretty wildly off, though I don't know about that individual one and my latest Litz book is packed away right now.
This was my first assumption in the field, but I posted on the Reloading forum here and Mule Deer responded quickly that the BC was actually very close on that bullet according to Litz.
I was zeroed at 200 and the wind was almost non-existent (which is why we were sweating so bad......August is not the best time to shoot in MS). When we did get a slight breeze, it was in our face.
AH64guy, it's interesting that your MOA calcs are almost exactly how much I was off at 800. What program is that?
I hope to get to go back to this range soon and try again. We all had a lot of fun as none of us had ever shot anywhere near that far.
