What would cause this? Bullet drop with elevation change

[Jpron]

Having read the entire thread, I would venture to state the obvious, the only thing that would affect all six rifles would be environmental. So for me we would have to know the precise figures. The big problem I have is where were all six rifes set up...if they were not set up in the same area with the same environmental conditions, then they should have seen a different drop, something other than two inches for everybody...so taking a WAG it would seem to me that at the target there was a pretty good wind forcing the bullets down...microburst if you fly, and for me that is the only thing that would affect all six rifles at the same time. A good thought provoking thread for sure.

I should have been more clear, they are are low, but not all 2 inches. He said they were different amounts low and at different distances. It is an environmental effect, I'm trying to figure out what

 

[26Reload]

Earth's axis rotation disorientation...
Ha...
Bigfoot sittin' off to side sending messages into shooters head....
"The Biden Effect".....feeling yourself falling from grace of gun ownership..causing focal disorientations...."oh, come on man"

 

[wkdwdg66]

Just throwing this out there. I've read all the reply's on temp. So certainly worth looking into. Different rest, could be. But I would throw out that powder will burn at different rate at 860 ft vs 7200. Especially if cold. So much less Oxygen at 7200. Rate of burn slows and velocity falls off slightly. Cold temp and less O2 to fuel the burn equals slower velocity in any textbook I've ever read.

O2 not a factor for burn rate, please reread the books.

 

[doubledoc]

I mounted a scope and developed a load for a friend of mine. I'm at 850 feet of elevation. The gun was shooting great when he left. I had it zeroed at 100 yards. He got to his elk hunt today. He is 2 inches low at 100 yards and is at 7200 feet. He dialed the correct moa and tried at 350. He his 6 inches low. He's the clinker, there are 6 guys on this trip and everyone of them is seeing the same thing. Higher elevation shot be less bullet drop but not in this case. The gun is a tikka 300 win mag, h1000 powder, 200 gr eld-x. Temps are similar to when we shot here. Anyone have any ideas?

If you haven't seen the targets yourself, be skeptical. Six rifles, all different, different calibers, shooters, techniques, ALL SHOOTING EXACTLY 6" low???? I just kinda doubt it's going to happen no matter what......

 

[cohunt]

I think the answer is on post #65 -- says shooter zeroed and shot first from a leadsled -- yes it also says he then shot off bags and made hits ( but he was shooting milk jugs so he could have been off zero and not known)

Sounds like a leadsled problem to me, those things are bad news in my eyes

 

[Big Turnips]

Moral of the story...It's always good to check your rifle's zero when you arrive at destination before your hunt.

 

[Philward]

This seems more believable since all guns are doing it.

Agree, but...how difficult is it to tell the difference between 100yds and say 175, 200. I suppose if you haven't done much shooting you wouldn't know the difference. I was considering 100yds and 100metres but that is only a difference of 9 yds which shouldn't account for a 2" drop.

 

[HRM Johnny]

So just out of curiosity what type of range facility and benches are they using at elk camp ? Are the targets on the same plane as they were where you sighted in at not up or down angled from at the home range . Is it close to the base of a cliff , or maybe in a canyon or large draw ? We have a lot of changing air currents where I live when you are at the base of a cliff depending on the direction of the wind hitting the back side of the cliff you can have a down draft or if it's blowing toward the cliff face on your side you can have an updraft . Down in Colorado at the Bolder air port they have what are called rotators that are similar to a tornado laying on it's side but you can't see them with your eyes as they don't pick up any ground litter and before they learned what was happening there were several small planes that just all of a sudden nose dived dropping several hundred feet in seconds . Perhaps something of this nature is happening so that there is a hard downward wind between the shooter and the target . Just some thoughts I had from some of the things I've seen in the mountains that people from other places may not have seen yet .

think the answer is on post #65 -- says shooter zeroed and shot first from a leadsled -- yes it also says he then shot off bags and made hits ( but he was shooting milk jugs so he could have been off zero and not known)

Sounds like a leadsled problem to me, those things are bad news in my eyes

@cohunt, that only accounts for the one shooter. If there are six people experiencing this, there has to be more to it. The only thing I've heard that makes any sense so far, is post number 23. I copied above. Having thought about this some: if it is something like @DSheetz brought up, I would think that it should have been seen before. @Jpron, has the outfitter ever seen this phenomenon before?

 

[FEENIX]

Moral of the story...It's always good to check your rifle's zero when you arrive at destination before your hunt.

Yep, that is what I noted in #13.

 

[Bang4theBuck]

My opinion is that there are multiple possible causes for the poi shift. I dont believe that air density had anything to do with the 2" poi shift at 100 yds. I believe that it was technique. It was either the rest, or something affecting barrel harmonics. First, technique.....how many times have we been on hunts or at fun shoots and you have an improvised rest of some sort? Once the first guy in a group of buddies sets up a certain way and takes a shot (across the hood, on the tailgate, with/without a lead sled, across a backpack, etc) and then the rest of your buds do the same thing, as it seemed to work. This could explain why everyone in the group was low at 100 yds. As for being low at 300 yds, this needs to be looked at from two perspectives. First adjust your zero to be right on at 100. Now check your impact at 300. If 90+% of your issue is gone....great! Now just analyze what it causing the 10% shift at 300. All of the possibilities related to environmentals and internal ballistics are potentially relevant again in solving the problem at that point.

 

[Jpron]

@cohunt, that only accounts for the one shooter. If there are six people experiencing this, there has to be more to it. The only thing I've heard that makes any sense so far, is post number 23. I copied above. Having thought about this some: if it is something like @DSheetz brought up, I would think that it should have been seen before. @Jpron, has the outfitter ever seen this phenomenon before?

I have not heard from my friend since that evening. This is not a lead sled issue. There is an environmental factor here , but what is it?

 

[Ckleeves]

I really don't think it's environmental. Run the numbers anyway you want, from sea level to 14k and try to throw in as much temp and humidity change as you can. You can't come up with 2 moa off zero at 100. As far as a increase/decrease in velocity due to temp you would have one picky load/barrel if a 50fps swing causes a 2 moa shift at 100.

Breaking in barrels and doing load development I have shot sub 1" groups at 100 with loads that have 200 FPS + of swing. Not all the time but it does happen.

As others have said I would be taking a hard look at parallax, what rest was used, rear bag, possible barrel contact in the channel from different bipod loading and (I'm sure other will disagree and this is just my opinion) the Vortex scope on top if that's still what's on it.

 

[swe123]

Different angles at different sites?

 

[Stevenstl86]

Was the target was an extra 50-75 yards out?