What would cause this? Bullet drop with elevation change
- Thread starter Jpron
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I have not talked to him since that night. I gave him a couple different options. He said the grouping was fine. Just low.
hunterbob
Well-Known Member
Sounds like rifle was zeroed at 50 yds , and never got fine tuned at 100 , 200 or 300 -to 500 yds ...This is what happens, and if the load isn't ... air density also has a lot to do with ballistics.
sea2summit
Well-Known Member
Could be part of it but I'm thinking humidity plus temps. If he's down at 800' with 80-90% humidity then goes to 7k with 30-40% that could be about 2" difference depending on the cartridge but that would be on the high side at 100 yards.
Hugnot
Well-Known Member
Goes to show, zero in upon arrival. I have zeroed in rifles near sea level, in cool temps and rain and gone out to shoot rodents at 5000' plus at 95* in blazing dryness (check this out with a ballistic calculator like Hornady 4DOF) and never experienced huge changes like 2 inches at 100 yards. Sounds like all 6 guys had problems with their rifles, scopes, mounts, stock bedding, ammunition, and shooting caused by transport or demands to shoot at unfamiliar sites. Also, the rifle was zeroed at 100 by a certain shooter then transported to a distant location and shot by another different shooter with different results - sounds like an addition of a huge amount of variables. Takes me back to an experience where I drove about 300 miles to hunt and other hunters flew in. The outfitter wisely had everybody shoot at a 250 yard target and the misses were extreme, like 6-8 inches (high, low, left, right), all caused by equipment problems or human error.
Capt RB
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It's not. Take a look at density altitude. I shoot alot in winter at 34' above sea level. My typical DA is -3500' at 20 degrees. Using 60 degrees with a dew point at 58 the DA would increase from 800 to 12XX'. Using 7200 20 and 0 for dew point you are more than double signifying much better ballistics downrange. They lost 2 minutes on there 0 which would be the 6" at 300 yds if they didn't add that 2 minutes back before correcting to their 300yd dope. I had a 2.5 moa zero change when I went from Ft Lewis to Germany. I had a 1moa change from the post in Germany to the winter training area in Hornsfel Germany. I had a 1moa change when I went to the desert. The dope changes some based on DA and the zero changes in some cases. Today I would say that the differences in Lattitude have far more to do with changes in zero with the information available that pertains to the angle of the sun. IE the light is being bent slightly different making your optical system project your reticle in a different place than where you zeroed the rifle. You can log this at your range by shooting morning noon or night. Another eye-opener is when it is bright and a cloud blocks the sun watch what happens to the bullet on the same hold.
sea2summit
Well-Known Member
Not talking just altitude density. Rule of thumb is 20% change in humidity is about .5 MOA. Increasing humidity leads to more efficient bullet flight, decreasing it will fall. So if he's at 80% and goes to 20% you'd come close to the 2" drop in POI he's talking about. But jumping up in altitude will increase the POI so I can't justify the whole 2".
Capt RB
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Here is very basic information on how light refraction will change the location of an image
Atmospheric refraction - Wikipedia
Your humidity statement is correct if you are shooting the same condition at the same location minus the humidity. Once you change altitude you would correct off of the zero condition for that load. I use da because I know from my dope how to adjust as the weather changes. Although I always noticed and recorded how my zero would shift from morning to midday to dusk I didn't know why until I read an article by David Tubbs time of day changing his zero at Camp Perry. Ask a surveyor they will have a book on it as they are recording data every day in every weather. They can explain it far better than I can
I have. Please reread my other post.
I very clearly stated it was "just throwing it out there" as "wormholes" were jokingly being thrown out there. The point was given, all most obvious reasons for trajectory difference was covered, I was suggesting something quite outside the box. I acknowledged the far reaching nature of the supposition. In the future please attempt to gather all the info prior to responding.
Hugnot
Well-Known Member
We are talking about 2 big inches at a short 100 yards. Logically at 3.5X the distance or at 350 yards it would be 7 inches more drop (3.5 * 2). The OP uses the well known Hodgdon extreme powder H1000 and temps were "similar". The Hornady 200 grain ELDX bullet was used.
I have never experienced stuff at real short ranges like 100 yards, caused by temperature, refraction, wet air, or elevation. Taking a look at the Hornady 4DOF calculator this comes down to some 9.31 MOA needed for 500 yards @ 90% humidity & 820" elevation. At 500 yards at 10% humidity & 7200' elevation 9.32 MOA needed to connect. Both with a 100 yard zero. This is only .01 MOA difference. Are the Hornady 4DOF Doppler radar calculations to be trusted?
On a past operation, going from my former, friendly, wet, sea level range near Seattle, USA to the blazing dry, hot, mile high rodent grounds of Wyoming, USA I did not need to re-adjust my cheap Weaver Grand Slam 6-20X40 scope to achieve multiple hits on the rodents. In fact, taking a target stuck to a cardboard box with rock inside so it would not blow away, my chosen 1 inch high zero at 200 was verified at a laser measured 200 yards. This is for a .22-.250 shooting 55 grain Sierra GK's at 3600 +-. My rifle had a nice Lilja #5 barrel, free floated, action and barrel shank carefully bedded in a laminated stock, front action screw at 60 inch/lbs. , scope in Ruger rings at 60 in/lbs. at receiver.
All this appears, to me as conjecture (there is not enough info) is driving this discussion. At least, I would not have somebody else sight in my rifle. It sort of appears like some kind of multiple user screw-up. Was the shooter aiming directly east so the spinning earth would move his zero away increasing the distance? (not likely with TOF measured in fractions of seconds).
I have never experienced stuff at real short ranges like 100 yards, caused by temperature, refraction, wet air, or elevation. Taking a look at the Hornady 4DOF calculator this comes down to some 9.31 MOA needed for 500 yards @ 90% humidity & 820" elevation. At 500 yards at 10% humidity & 7200' elevation 9.32 MOA needed to connect. Both with a 100 yard zero. This is only .01 MOA difference. Are the Hornady 4DOF Doppler radar calculations to be trusted?
On a past operation, going from my former, friendly, wet, sea level range near Seattle, USA to the blazing dry, hot, mile high rodent grounds of Wyoming, USA I did not need to re-adjust my cheap Weaver Grand Slam 6-20X40 scope to achieve multiple hits on the rodents. In fact, taking a target stuck to a cardboard box with rock inside so it would not blow away, my chosen 1 inch high zero at 200 was verified at a laser measured 200 yards. This is for a .22-.250 shooting 55 grain Sierra GK's at 3600 +-. My rifle had a nice Lilja #5 barrel, free floated, action and barrel shank carefully bedded in a laminated stock, front action screw at 60 inch/lbs. , scope in Ruger rings at 60 in/lbs. at receiver.
All this appears, to me as conjecture (there is not enough info) is driving this discussion. At least, I would not have somebody else sight in my rifle. It sort of appears like some kind of multiple user screw-up. Was the shooter aiming directly east so the spinning earth would move his zero away increasing the distance? (not likely with TOF measured in fractions of seconds).
Stevenstl86
Well-Known Member
2nd focal plane scope sighted in at less than full magnification? 
I know all 6 rifles couldn't fall into that
I know all 6 rifles couldn't fall into that
mpayne
Well-Known Member
It might be too much bourbon at higher elevation, it has been know to put a whole hunting camp on the wrong course for days!
