James B

I was reading on another formum about missing shots at deer and it brings to mind again a problem I had last year as well. Where I live, I sight my rifles about 2 1/2 inches high at 100 yards but this year and last year as well, my first couple shots were high enough to miss a deer. I was reading an artical by Craig Boddington about long range shooting and he commented on elevation having affect on trajectory which of course makes sense. He did not however have any rule of thumb for elevation difference. There is about 2000 feet difference in elevation between where I live and where I hunt. I quess I never thought that would be enough difference to have to change the setting on my scope. I have shot a lot of long range Silhouette shooting but it was always at about the same elevation. Does anyone have any thoughts on this. There is surely several inches difference in my trajectory where I live to where I hunt. Some of it could be a difference in estimating range from the flat country where I shoot and sight in but there is some difference in trajectory as well.

cdr4thBn

I think I might be able to provide you with a little additional information. You didn't mention the caliber, bullet weight, muzzle velocity or the actual elevations you're shoting. I ran some easy numbers thru one of my ballistics programs and came up with the following information.
At 1000 feet of elevation above sea level, a 300 Win Mag firing an 180 gr bullet at 2960 fps that is 2.8'' high @ 100 yards has a zero at 250 yards. The highest point of trajectory is at 150 yards where the bullet is 3.3 inches high. At 300 yards the bullet is 4.0" low. So theoretically, if you shot it down a pipe 300 yards long and 8 inches round it wouldn't touch the pipe. Your pointblank range is about 300 yards.
Now we'll climb up to 7400 feet above sea level.
The same 180 gr. bullet traveling at 2960 fps will be 2.8" high at 100 yards. 3.0" high at 150 yards. Zero at 250 yards give or take a statistically insignificant distance. And be 3.7 low at 300 yards.
For all practical purposes the reduced air pressure has maintained an almost identical point blank range. So it doesn't look like the 2000 feet of elevation change would have the effect you suspect. I would suggest that the problem might be in your range estimation or something akin to it.
I hope this helps a bit.

turtle71

Were these shots uphill or downhill? That can make a shot go high.

James B

Thanks for the info. I was shooting a 257 Roberts with the 100 grain Barnes X bullet at 3129 fps. My two missed shots this year were at about 200 yards. Slightly down hill. I sighted the rifle in at about 1200 feet above sea level and was hunting at about 3000 ft above. I would not think with the info you have that this could be all of the problem. The land is quite hilly and up or down angles could be more than a person would realize. I also may have been a little higher on target here when I zeroed it. I have since gone to setting my POI about an inch high at 100 yards. I have read that one usually misses high when they miss. I certainly fit that profile. Thanks again.

bigbulls

Yes James, there is very very little differance in POI at different elevations. One could actually experiance the same changes in air density at a single elevation depending on how hot or cold it might be on a particular day. My rifles are sighted in at about 5500 feet above sea level and I hunt anywhere from 8500 - 11000 feet above sealevel. I have not experianced any noticable differance in POI with as much as 5000 - 6000 feet difference.

I sight my rifles to hit 1.5 inches high at 100 yards. I know that on an deer that is good to about 250 yards +/- with no hold over.

James B

Thats about where I am sighting mine now. I didn't expierence the same impact difference with the 280 and it was sighted only about one inch high at 100 yards. I have a 3x9 Luepold on my 257 Roberts and a swift 3x9 on my 280.