I spent most of the summer getting set up to try for a deer at 1000 yds. I had shot deer and antelope out to 700 in the past but had never worked at it really. This year I had bought a new rifle, a Rem 700 Sendero in .264 WM and worked up my load using a 142 Grain SMK with it running 3170 fps with an ES of 15 over the Crony Chronograph. My scope is a Leupold MK4 6.5X20X50MM with the TMR reticule. I'm using Sierra 6 for the ballistic program. Leica 1600 LRF. Caldwell Wind meter. The first morning of my hunt I spotted across the canyon a big Mule buck and was able to range him at 768 yds. I got on the rifle and dialed in 14 MOA on the scope. Checked my wind meter and it showed a 4.5MPH wind directly from my 7:00. The deer was going on an angle roughly 45 degree's uphill to my left at a slow walk. I double checked everything again and slowly squeezed the trigger. I was able to get back on the scope and spotted my shot hitting about 5' below him and directly under his shoulder. My spotter called low and said up 2.5 MOA. I adjusted that much and again got on the trigger and squeezed off another shot. My spotter asked me if I had adjusted what he gave me as I was again under. He said give it another 2.5 MOA which I did. All this time the deer is still angling uphill and away from me. Again I get on the trigger and slowly squeezed the trigger. I was again able to get back on the scope and this time I spotted the buck do a huge jump and a belly kick showing me a good hit and then disappeared. I loaded another round and got back on the scope and watched as the deer was at the top end of a gulley that dropped down into the canyon and it was full of small trees and buck brush. Shortly after that I spotted it again but looking like it was trying to climb out of the gully and almost like it was standing on its back legs. Again I tripped the trigger and the deer again disappeared. I sat there watching along with my spotter for over 10 minutes and he did not show again. I finally told my spotter to watch and I was going to head off across the canyon and find the deer. After about 30 minutes of crawling down and back up the other side of the canyon and following what I thought was the right gully and going to the top of it I found I was about 1/4 mile south of the gully I wanted and headed that way. After a short time I came to the top of the gully and there in the bottom lay my buck. After making sure he was dead I waved to my spotter to figure out a way over and that the deer was down. (Took him 45 minutes to make his way over to me with a vehicle to pick us up) While I waited I checked to see where the buck was hit. My first shot had hit a bit back and had totally destroyed the diaphragm and the liver and left about a 2" hole going out. This is what caused the huge leap and belly kick. When the deer had attempted to crawl out of the gully my second shot had taken out both front elbows and put a 2" hole through the lower chest taking out part of the heart. Both shots would of killed him. Now here is the question. All summer I had been checking my drops all the way to 1200 yds and they had been pretty much dead on. The range I shoot at has about a 10 degree decline from where I shoot to 1200 yds. I almost always shot on nice sunny 50 to 60 degree days. I had checked and chrono'ed the load a number of times and was pretty sure I was correct. The day I was shooting the deer we had a storm coming in. Temps were about 17 degree's Humidity was 40 percent at the time and the shot was 19 degree's incline. My range is about 4500 in altitude and where I was hunting was around 3500. Can this differences account for that much more drop. I am really happy with my buck as he is a 6X7 Mule buck but was terribly unhappy with my drop's. Except for the drops everything else was spot on. Somehow I have to figure out something different to correct for this. During this hunt we had two guns shooting and both guns shot under. Something needs to be figured differently. I'm guessing that between when I ranged the buck at 768 and when I hit him the first time he had gone maybe 50 yds. this would account for some of the drop but not 5 MOA which at that range works out to almost 40"s of drop which by my chart works out to about 930 yds.