Missing on elevation Calculation

[Wyofax]

So I ranged a deer at 972 yesterday and set up the 264 win mag. My buddy had the tag, so I was running Shooter app and dialing while he was concentrating on straight easy trigger pull.

Here is the issue. I calculated a need for 18.25 moa with 2.5 left wind. We had a 9 mph wind from our 7 o'clock. The buck was bedded broadside angled just a bit away, sprawled out enjoying the afternoon sun. At the shot I watched the 140 Berger drop into my view through the spotting scope and sail right over the bucks back. The bullet hit in sage and I couldn't see the exact impact for elevation, but I thought it was about 2 MOA high.

Since I felt like 2 MOA was farther off than my calculations should be, I dialed down to 17.25 with the same wind hold and he sent another. This time I saw the bullet strike mid rib and the buck just laid his head over in his bed for a permanent nap.

My question is this. I feel confident that I have the bullet speed and BC correct because most of the time we are hitting spot on. The concern I have is that I am getting the environmental calculations wrong. I have gone back into Shooter and made alterations to the conditions that push me closer to what we dialed, but the closest I can get by changing factors to the extreme potential at that exact moment is 17.5.

Some of the things that I am talking about changing are barometric pressure, elevation, temp, humidity. The one thing that I cannot factor is the human element of my friends potential affect on bullet impact.

What are your thoughts?

By the way, the bullet entered middle body between the 9th and 10th rib. Destroyed two major lung lobes, angled up and broke the spine and a rib where it attaches to the back and stopped against the skin on the backside. Bone fragments exited the body and he was lying in a puddle of blood. Just under 2000 fps impact velocity with just under 1240 lbs at impact.

 

[dkhunt14]

Did you take all the parallax out and check by bobbing head side to side and back and forth. Parallax at that distance can hurt you. Was the mirage running up for thermals? Maybe the wind was running more towards target. Matt

 

[bigngreen]

A wind from 7 at that range was likely a little stiffer at the top of the trajectory which would put you high, Coriolis could add a 1/4 depending on direction, buddy shoots a little looser on the rear bag, range finder picked up something a little closer.

When this stuff happens I take the time to shoot a few more rounds at something near by till I get it figured out cause that is your ONLY chance to know for sure the cause!

 

[BrentM]

I was thinking the same thing as bigngreen. Shooter can have big affect on this. Unless he holds that rifle exactly the same with similar eye alignment as well as hold to the shoulder it could affect things enough.

Did you account for coriolis? I add or subtract .3 for 1000 yard shots for a 140 vld at 3020 fps.

A 7 oclock is basically to your back and I aslo suspect lifting up the face of the hill he was bedded on. So, a little more speed perhaps down range, plus uphill wind which lifts the bullet a little.

Besides the obvious atmosphere stuff this is something I would look at. Temp, absolute barometric pressure, coriolis, wind speed/direction and lift.

What you think?

 

[mrb1982]

I am tagging this because I see what you are saying and I am curious to hear more experienced guys then me comment on it.

I had two hits between 580-600 this weekend. My buddy was behind the gun at 900 and I would have liked to tried it myself because the gun is set up for "me" so I shoot it pretty good, but if others, as mentioned before, don't shoot the same way as I do, then it probably isn't going to hit the same.

My guess would be as previous mentioned, the cheek weld pressure, or possibly the amount of preload on the bipod?????? Who knows. If you consistently have it figured to a good velocity, and are hitting the conditions right, I am guessing it has to do with shooting style more. I am interested to hear others chime in though.

 

[Wyofax]

This is great dialogue. So a little more info as you all are asking great questions. I did not check parallax since I was not behind the gun, but I should have. I did turn on spin drift and coriolis so I think that was accounted for.

I did my best to read mirage and it appeared to be laying almost flat, but that is a difficult thing to master.

Our shot was across a creek bottom but even more distance was traveled down the creek than across and the hill he was laying under wasn't very high. I didn't feel like there was much opportunity for wind lift in this situation but it was a possibility.

Funny that it was mentioned about range accuracy because I messed that up last time out so it was front of mind on this one. Fortunately he was bedded in a sage pocket and I ranged it about 5 times bouncing it a little high and a little low a couple times to make sure I was right on. When I went high I got a 979 reading and 969 when I targeted a little low, so I was very comfortable with the 972.

I was very happy with the wind read. On Shooter I used the arrow for direction selection and my wind meter for the speed. I was getting a typical variable reading between 5 and 9 mph at 217 degrees based on the target at 180. With the first shot a miss, the windage read was spot on, so I had him maintain the same 2.5 MOA hold. With that somewhat variable wind I selected the highest read since I assume there is more wind aloft than at my ground level.

 

[Scot E]

What was the terrain like where you were shooting? A 7 o'clock wind with some terrain change could easily result in a 2 MOA change at that distance.

Scot E.

 

[Wyofax]

What was the terrain like where you were shooting? A 7 o'clock wind with some terrain change could easily result in a 2 MOA change at that distance.

Scot E.

So we where shooting in a sand dune. Sitting about 200' elevation above a creek bottom and the buck was bedded about 30' above the bottom on the other side of the creek. The dunes fell away from us toward the bottom and just a small rise to the deer.

 

[Scot E]

Was he straight across from you, as far as the creek bottom and lay of the land goes or was he above or below your position? Was that 7 o'clock wind blowing up or down the creek bottom? I assume you had your incline/decline correct for that shot? The reason I am asking all of this is because those type of winds will play havoc with my elevation where I shoot but I am more mountain type shooting. But if you had some elevation change, which you did, and some wind pushing your bullet up, with a funky wind I have seen some pretty steep changes in POI.

 

[kcebcj]

edit Scott above posted at the same time as I and touches on slope)

It has not been mentioned unless I missed it but was the shot level or was there some slope. You did shoot high. Just a slight 20 degree slope (which is not much) at 925 is easily 2 MOA depending on the rifle and load. What was the corrected Horizontal Range when you ranged him?

 

[BrentM]

Good points on slope, that is why I shoot almost exclusively for practice in the mountains in Idaho. Lots of elevation and slope changes with wind readings that create mental issues for the sane person.

If you didn't account for the correct slope and wind to your back you would have mis-read for sure.

 

[Wyofax]

So guys the slope was something that I didn't account for but probably was one issue that had a small affect but it was only a couple hundred feet drop across almost 1000 yards. So minimal affect.

 

[BrentM]

Probably 4%. All slope for long range should be accounted for. All these things are part of the math equation.

 

[Broz]

Mis-range from the RF or soft rear bag allowing but to drop on recoil.

Jeff