What would cause this? Bullet drop with elevation change

Jpron

Well-Known Member
Joined
Feb 10, 2019
Messages
117
Location
Wi
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?
 

phorwath

Well-Known Member
Joined
Apr 4, 2005
Messages
7,140
Location
Alaska
His rifle zero has changed since you sighted it in, or he shoots the rifle to a different POI than you.

As to each of the other rifles in camp doing the same thing, I doubt it. Folks should zero their own rifles prior to their hunt. The fact that one didn't leads me to doubt their consensus conclusion that all of their rifles have been jinxed. It'not gonna happen coincidentally. Only if someone sabotaged each and every rifle, or is the master of voodoo.

Just my opinion. Throw it away if you don't like it.
 

MTbackwoods

Well-Known Member
Joined
Mar 5, 2020
Messages
275
Location
Montana
I shoot prone with a bipod and rear bag 99.9% of the time. That’s how I sight in all my rifles. On the occasion I shoot from a bench, with the same bipod and bag, my poi is different. Even changing bags in the prone will cause different poi. So my guess is he is doing something different or using something different. If he and you have proper training and use proper technique, the poi should be almost identical between the two of you. I’m gonna say it’s his technique or equipment that’s causing the shift
 

gearguywb

Well-Known Member
LRH Team Member
Joined
May 7, 2020
Messages
282
Location
KC
A POI shift is to be assumed when going from less than 1000 to over 7000 elevation. Another factor not noted was the temperature when zeroed compared to the ambient temp at the hunting spot. Both of those factors will definitely effect velocity, which in turn will change the POI.
 

VLD Pilot

Well-Known Member
Joined
Dec 24, 2017
Messages
1,783
Location
Northern, Mi
That's an odd one for sure. I think 2" at 100 yards Is huge. Definitely too much even if it's high and elevation is 10,000 ft. It wouldn't change that much at 100 yards. Odd thing is all the rifles are hitting lower at higher elevations. Wow. Head scratcher for sure. There's obviously an explanation. Post your findings please. Temperature wouldn't change POI that much either at 100 yards. That change comes from velocity changes and 100 yards is much too close to make that much difference. If this 2" drop was at say 300 yards, I'd say that's more realistic .
 

VLD Pilot

Well-Known Member
Joined
Dec 24, 2017
Messages
1,783
Location
Northern, Mi
Man it's gotta be something else. There's only maybe a 20-25 fps difference in velocity at 100 yards between 0° and 80°F at that elevation. Not nearly enough even to move the bullet a fraction of an inch.
 

Capt RB

Well-Known Member
Joined
Dec 1, 2014
Messages
1,880
Man it's gotta be something else. There's only maybe a 20-25 fps difference in velocity at 100 yards between 0° and 80°F at that elevation. Not nearly enough even to move the bullet a fraction of an inch.
Some of the stable powders are .5fps per degree when optimized. however, others can be 1.4-2per degree. and that is not linear. It might be that in the first 15 degrees then due to pressure dropping off goto more than 200fps in 50 degree changes if a hotter primer or more neck tension which then changes everything. I've done alot of cold weather load testing over the years and it can be enlightening to say the least. Ask the 300 rum guys what happens with Retumbo below 0. Hasn't happened to me yet but if it bridges it will minimum lock the gun up
 

FEENIX

Well-Known Member
LRH Team Member
Joined
Dec 20, 2008
Messages
16,421
Location
Great Falls, MT
One rifle can be explained very easily but 6 I have no clue hope some one chimes in with an answer to this
Agreed!

@Jpron, try plugging in the load information on Berger's ballistic calculator (https://bergerbullets.com/ballistics-calculator/). The drop should be lesser at higher altitudes (i.e., 350Y drop @ 850' vs 350Y drop @ 7200'). If I ran one of my .300 WM, 190g Berger VLD 3043 MV, I get the following drops ...

350Y @ 850' = -15.68"
350Y @ 7.2K' = -14.91"

Also, please verify if he is 2" low vs. 2 clicks low @ 100Y and 6" low vs. 6 clicks low @ 350Y, just throwing it out there.

In either case, it never hurts to do final sight-in at the actual hunting grounds.
 
Last edited:

VLD Pilot

Well-Known Member
Joined
Dec 24, 2017
Messages
1,783
Location
Northern, Mi
Some of the stable powders are .5fps per degree when optimized. however, others can be 1.4-2per degree. and that is not linear. It might be that in the first 15 degrees then due to pressure dropping off goto more than 200fps in 50 degree changes if a hotter primer or more neck tension which then changes everything. I've done alot of cold weather load testing over the years and it can be enlightening to say the least. Ask the 300 rum guys what happens with Retumbo below 0. Hasn't happened to me yet but if it bridges it will minimum lock the gun up
I get that scenario but he's talking about 2" at 100 yards. Elevation increase of over 7000 ft also should cause a higher impact. Something is going for sure and it's happening to all their rifles. Obviously it's an environmental issue or pressure issue probably related to environment
 

Primary

LRH Assistant
Here are some related products that LRH members are talking about. Clicking on a product will take you to LRH’s partner, Primary, where you can find links to LRH discussions about these products.

 
 
Top