No, not drastic. Actually very little change at 420 yds inside of 2-3000 elevation change.
NOW, 700 yds and a 6000' elevation change can cause a miss.
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Scope field evaluations on rokslide
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NOW, 700 yds and a 6000' elevation change can cause a miss.
Hmmmm that wasn't my experience at all going from 1250 ASL to 4800 ASL on my Wyoming hunt.
Guide required us to shoot when we got there. My zero was still the same on both rifles.
7.62 Gunner
Well-Known Member
The problem with using a drop test as an absolute is that there are fluctuating variables that can't necessarily be accounted for.
You can make any scope fail to hold zero depending on the surface and point where impact is initiated.
For example I recently knocked my rifle off my work bench while messing with the bipod, the March FX 4.5-28 has passed all kinds of impact tests I've done but not this time..
That's cuz it impacted on the eye piece and shifted the optic in the rings, wouldn't have noticed the movement had I not put witness marks on with a fine tip sharpie.
Zero shifted approx 6"
This year a buddy had his cheap sling break and dropped his rifle in the dirt scope first, he missed a cow that night and I thought 100% he'd lost zero. It was a leupold so that's automatically where I went
We tested his zero and it was perfect! I scratch my head about it until he opened the mag and dumped a bunch of dirt out..
Point being I never ever expect any scope to be okay after a drop without testing it first, and checking out the barrel!
Here's a pic of the dent on the left side of my scope cap from impact
You can make any scope fail to hold zero depending on the surface and point where impact is initiated.
For example I recently knocked my rifle off my work bench while messing with the bipod, the March FX 4.5-28 has passed all kinds of impact tests I've done but not this time..
That's cuz it impacted on the eye piece and shifted the optic in the rings, wouldn't have noticed the movement had I not put witness marks on with a fine tip sharpie.
Zero shifted approx 6"
This year a buddy had his cheap sling break and dropped his rifle in the dirt scope first, he missed a cow that night and I thought 100% he'd lost zero. It was a leupold so that's automatically where I went
We tested his zero and it was perfect! I scratch my head about it until he opened the mag and dumped a bunch of dirt out..
Point being I never ever expect any scope to be okay after a drop without testing it first, and checking out the barrel!
Here's a pic of the dent on the left side of my scope cap from impact
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Your 100yrd zero won't change. But using your values and standard atmosphere numbers the further you shoot the more drastic the change.
Your 500yd impact would be 3" different solely from density altitude change from 1250 to 4800 (just using a 308 load I have in the gonkulator).
Where I hunt at 9500' the difference is 6".
The difference is greater at further ranges too. Inside of 300yds won't make a difference.
Sometimes you will be surprised. A drastic change in humidity can sometimes effect trajectory. I don't know that I have ever seen 6 inches but I have seen a 2-3 inch difference. I live on the gulf coast and have traveled to Missouri and had to RE zero. Let me correct that! Not necessarily re-zero but adjust my dope down range. The decrease in humidity can make a difference. As you climb in elevation the air gets thinner. You are correct that it is usually at extreme elevations but it doesn't always have to be, that is the reason for humidity and barometric pressure inputs in your ballistic calculations. If you are certain it is scope shift get a set of Hawkins Precision they are light and just work. I am running them on four of my rifles. JMTs
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It is air density...
Not air density or elevation. My 20 ft elevation here in nc was 2 inches off at 7500 at the NRA center in Raton where i rezeroed. According to my kestrel same air pressure when i shot. Think about it, my zero would have shifted right and up permanently.
Still going…. Although the opinions vary, this has been a good reminder of things that can impact POI in hunting situations. Clamping ability of rings ranks high IMO. This combined with the ability of the scope tube to withstand sufficient pressure from those rings is something many don't consider. I was shocked to find out that high end scopes like TT recommend only minimal torque values on rings. This has changed my wish list for my a future scope. Great glass is very pleasing to me. However, delicate scopes have no place for me in a rugged hunting scenarios.
Then why did your impact shift?
Argon Glen
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All other environmentals being equal, humidity has the least impact. For example (using JBM's defaults and only selecting a bullet from the dropdown):
Hornady 308 ELDX 212 grain at 1000 yards
| 249.2" | - drop at 0% humidity | |
| - | 248.4" | - drop at 99.9% humidity |
| 0.8" |
To be clear, that is less than one inch over 1000 yards.
Physics are in play all the time. They don't decide one day to have effect and the next day decide not to.
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I wasn't trying to get into a specific amount of drop or point of impact just that it is all apart of the equation and when you consider all the variables effecting a bullets trajectory, humidity being one, barometric pressure another, altitude and air density a third, that you can have a point of impact change as well as needing to recalculate your dope. Just a few hundred miles of distance and a few thousand feet in elevation can change your point of impact and dope. Even if their is no point of impact shift your dope could be off by several inches at 600 yards. On a deer size animal that could translate into a miss. What concerns me in this discussion is all these scope malfunctions and POI shifts that so many are claiming to experience. In forty years I have broken two scopes total and both were my fault or due to improper mounting and maintenance. I have traveled for hunting and competition for years owned probably 100 scopes or more and other than having to readjust my dope or poi due to atmospheric conditions only ever had one time that I can remember having to realign a scope. I have a 1970s model Marlin 336 with a 25 year old Pentax 3-9x40 on it. That has been shoved between the seats of a truck and ridden around every God forsaken road in the country, dropped, sloshed through the mud, carried up mountains from Alabama to Michigan from Texas to Florida and everywhere in between and has not once had to be readjusted or lost its point of aim. Gun won't shoot a 2" group but has been used to kill more deer than I can remember. First rifle I ever owned. Today it is my loaner. Some one shows up without one here you go. If there was ever a scope or rifle that should have lost its POI it should be top of the list. The whole blasted set-up might be worth $400. We are talking about tier one set ups that cost thousands. Something just doesn't add up? Not that stuff does break but most people aren't that rough. One I can understand. 20 or 30 give me a break! Either you can't shoot, your mounting it wrong or something changes in the environment. Just my thoughts and again experience. I am not to rough on my stuff but I don't treat like a cup cake either. It is a tool and I expect it to work when I need it. 99% of my missed were not equipment failures but user error!
Impact somehow knocked it off
Argon Glen
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Fair enough, but that's not what you said which is why I replied the way I did. What you said was "A drastic change in humidity can sometimes effect trajectory." I simply highlighted the error of that statement. Not to challenge you, but to be clear to less knowledgeable people that may read your post.
Of course if the other environmentals are also changed a difference can be seen. Just depends how much of what is changed as to how much impact there is.
