Z6 Problem at elevation

[Short Track]

My Z6 preforms flawlessly at sea level.
I go mountain hunting at 10,000' Rifle starts shooting low. 2" low. should be shooting high at elevation !
Back to sea level, rifle is perfect out to 600 yards.

 

[Tra3]

Lots of missing data here.
Same ammo?
Same distance? (Measured?)
How many times have you completed this elevation change?
Similar temperatures?
Did you shoot at a range at 10,000’ with the same rest?

 

[BRICKBURN]

Temperature, was my first thought.

If all else is the same, the scope will be getting some warranty work.

 

[coreydb]

Altitude makes a big difference in zeroing adjustments. Download a bullet/shooters calculator software program like Hornady's; just to name one, and fill in the blanks to obtain correct zero settings for altitude, temp and humidity.

 

[Short Track]

Lots of missing data here.
Same ammo?
Same distance? (Measured?)
How many times have you completed this elevation change?
Similar temperatures?
Did you shoot at a range at 10,000’ with the same rest?

exact same ammo, same lot #. same distance, I repeated this problem. I can't even trust the rifle at elevation. The only variable is the temperature. I can't control the temperature. I think it's the scope, can't be sure. I even had a sea level gun smith go through the entire gun. and he shot it out to 600 yards personally.

Going to 10,000' gun should shoot higher, not lower.
Maybe it's something with the internal pressures of the scope.
That's all I can think of.
Otherwise it's a flawless Z6

 

[Altitude sickness]

A pressure difference (even if the scope is leaking) should not change POI.

the PSI difference from sea level and 10,000 feet is about 4 psi.

The total volume of air in the atmosphere weighs 14.7 pounds at sea level. And all the air above you pushing down on you at 10,000 feet weighs about 10 pounds.

if you have a leak in the scope you should also see some condensation.

A quick test would tell you if you have a seal leak. put a weight on the scope and lower it to about 9 feet of freshwater that’s the equivalent of 4 psi pressure change your are experiencing at 10,000. If it doesn’t leak you’re OK. if it does, it should be covered under Warranty


What type of stock does it have. Are you getting barrel contact?

Did you remove and reinstall the action into the stock at 10,000 ft? Perhaps not torquing to the proper specs.

Bad or defective scopes are most often. Bad and or defective scope mounting.

 

[SaintPanzer]

I don't "know", but I have a theory, take it for what it's worth.

I'm assuming the belief that POI should be higher is because the air is less dense?

But here's the thing: The powder is burning to provide the gas expansion that launches the bullet. At 10,000 ft, you have a lot less oxygen to feed the burn. This would lead to less expansion, and I would assume less velocity, and therefore a lower POI.

Do you have a chronograph? I'd be curious as to velocity at different altitudes.

 

[mark-hunter]

Do you use ballistic calculator, and do you use ballistic turrets on the scope?

 

[Short Track]

I have 2 rifles I travel with. Z6 6.5CM & Z8 .308.
The Z8 (.308) holds theory that the air is less dense, and POI is 2" higher.
The Z6 (6.5CM) does not hold theory. and drops 2". Otherwise, it's a dead accurate sea level Tikka out to 600 yards.

 

[Short Track]

Do you use ballistic calculator, and do you use ballistic turrets on the scope?

This was at 100 yards !!

 

[Altitude sickness]

Did you remove the action from the stock and reinstall at 10,000 feet without proper torque?

 

[Short Track]

Did you remove the action from the stock and reinstall at 10,000 feet without proper torque?

no. I remove the magazine, and load ammo. I'm not a gun smith.

 

[mark-hunter]

@Short Track
Oh! Ups! I was mislead by the point you made above, that at sea level performs well at 600 yards.

 

[JG26Irish_2]

I have had rifles that shot higher at altitude albeit not at 10k ft. I moved from 850ft elev to about 3750 ft and saw a few inches rise in POI on both 7mm/08 and 375HH at 100y. Both were zeroed about 2" high at 100y at home.

I have "Never" known of a scope issue that would affect POI that varies with elevation. Temp, ammo, mounting issues all could. I have a Z6i that has travelled with me from 850 elev to 3750 elev and saw a small change in POI in Limpopo that required a few extra shots to dial down the zero as it was shooting too high. My 308 remained as zeroed. My guess is you are using an ammo with a temp sensitive powder that is producing less velocity than it did at home at sea level but that is a SWAG guess as there are too many variables and not nearly enough information to diagnose remotely.

 

[mark-hunter]

he powder is burning to provide the gas expansion that launches the bullet. At 10,000 ft, you have a lot less oxygen to feed the burn.

No. This is wrong. Powder chemicals have oxygenerator element, which means combustion is selfprovided. You can shoot in vaccum, under water, in deep space, etc. (although not all such enviroments are safe to make this exercise, but cartridge will fire!)

Also, consider a barrel and chamber as sealed. Cartridge is sealed. Once the bullet starts to travel, bullet seals in front, and casing expansion seals at the rear.

 

[Hogpatrol]

Could be a rifle hold issue along with parallax. Look through the scope at a target, move your head up and down and take note if the crosshairs are moving.

 

[RedTag]

What was the difference in temperature between sea level and 10k feet elevation? Temperature is the likely culprit here. All ammunition is at least somewhat sensitive to temperature changes, some more so than others. I’ve tested various loads from 80 degrees Fahrenheit down to -40 and the differences can be staggering, sometimes with only 40 or 50 degrees changes in temperature.

 

[Bighorn191]

My Z6 preforms flawlessly at sea level.
I go mountain hunting at 10,000' Rifle starts shooting low. 2" low. should be shooting high at elevation !
Back to sea level, rifle is perfect out to 600 yards.

Like you said, it should be shooting high if anything...I live in CO and shoot at altitude a lot, At 10,000 feet, the DA can be crazy if you check it with a Kestrel. I was on a goat hunt a few years ago at roughly 13,500 feet and the DA was showing like it was 18,000 feet. That's the main reason I only use MOA or MIL turrets. I found out years ago that the yardage turrets only work well out to about 600 yards in various changes of elevation. But, your problem sounds altogether different. Thats a stumper.

 

[Philip Glass]

Are you using a Kestrel or range finding binos with the ballistics built in? How are you making your calculations?

 

[Ontario Hunter]

Some interesting info posted here. I vote for altered barrel harmonics. Check the barrel trough to ensure plenty of free floating clearance.

Over the years I have hunted in drastically changing weather conditions and was unaware extreme cold temperature could alter zero that much. However, I was almost exclusively a stalker/tracker in heavy timber and snow so shots were typically close range. These days I no longer hunt that way. Moose hunting here is mismanaged by fast buck idiots so I gave that up more than twenty years ago. Western Montana is an overrun hopeless mess of transplants and tourists. Good hunting there has gone the way of dinosaur. I hunt the east side now where shots are longer. My 30-06 is sighted in here at ~600 ft elevation usually in September but hunting in Montana I'm at +3K ft and almost always last week of November when it's very cold. Of course I always check my gun again just before hunting (that tiny town has a fantastic rifle range) and always wondered why the scope was usually off. Maybe I now have an explanation. I'm shooting 4350 or 4895 powders.