I shoot a 6.5CM, factory Hornady ammo. I zero’d my rifle at sea level with temps of 65 and humidity also about 65%. Took my gun to Montana for a hunting trip, temp 10, elevation 3500, and humidity about 65. My zero at 100 was 1.25MOA high. The elevation would make my bullet faster and the temp would make it slower correct? StrelokPro told me my bullet would be 125fps slower. It doesn’t make sense that my zero would be higher if the velocity was slower. I moved to 300 yards and my shot was indeed about 4” high. Turns out none of it really mattered as I shot my buck offhand at 100 yards so even 1-1/4” high wouldn’t make a difference but I found it interesting. Thoughts?
Temp and Elevation on ballistics
- Thread starter leclairk
- Start date
I did some calcs with ballistic AE using a profile for my 6.5 Creed rifle with a Hornady 140 and it showed the impact of the elevation change just cancelled the temperature change effect in your case so your zero should not have changed. I think the explanation lies elsewhere. If there is any chance that you were using 200 yds for one of them, I noticed the dial up for 200 with a 100 yd zero just happened to be 1.3 MOA.
I most definitely was using my 100 yard dope. I guess more will be revealed when I go to the range tomorrow and see what my POI is. I should be 1.25MOA low. If I am, I can’t think of anything else besides environmentals.
Yes. As molecules in the air will be further apart, thus, LESS friction on the bullet.
watercam
Silver $$ Contributor
In the end you did the right thing and made an adjustment. Even with access to all the mitigating factors in a computer it is imperative to check zero after traveling regardless. When I travel for long range competition I always check some kind of zero to get me in the groove regardless of conditions.
Temperature doesn't effect as much as elevation does. I'm at 700' ASL and shooting out west at 7500+ makes a huge difference. Turns a 7/08 just about into 7mm mag performance is here at home. As or more important, it allows a slower twist barrel to shoot what would need a faster barrel at sea level. Out to around 300 yards, the difference is not huge. Beyond 500 it does become big
Alright guys I am totally baffled on this one. This is the second year in a row that my zero has shifted when travelling to Montana. I went to the range today back home in Oregon and my zero was 2” high, should have been 1-1/4” low. The only thing I can think of is the way I transport the rifle for my hunting trips. I have a pelican case that carries my rifle and my shotgun. I noticed this trip that the bottom of my shotgun sits right over the elevation knob on my scope. There is a chance that during transport the shotgun stock bangs into the elevation knob. The problem with that theory is it’s not like I’m throwing the case around. I’m pretty damn careful with the case and it rides in the back of my suv. It’s a Schmidt and Bender scope so I would think it could handle it. Would contact with the elevation knob change my zero? The only time I use that pelican case is when I travel to Montana to hunt. Any other time I transport the rifle I use a single rifle case. Very interesting that 2 years in a row my zero changed by 3”.
Ned Ludd
Silver $$ Contributor
Certainly the act of traveling itself can cause a shift in zero, especially if the rifle setup is bumped, bounced, or jarred in some way during the trip. Nonetheless, traveling from close to sea level to several thousand feet above sea level can have a pretty significant impact on external ballistics. You have to be a little cautious simply looking at short range (~100 yd) zeros, which can vary to some extent simply due to the relatively short distance and because of how the ballistics calculator itself is set (i.e. whether you use std pressure at altitude, corrected air pressure, etc.), and may be harder to definitively relate to one another in terms of the change between the two.
A good way to see the effect of elevation is to simply set the calculator's zero to 100 yds for both conditions, effectively ignoring the zero point setting after that, and then directly comparing the predicted bullet drops at some longer distance such as 1000 yd. That is usually a very good illustration of how much less drag the bullet experiences during its flight at higher elevations.
A good way to see the effect of elevation is to simply set the calculator's zero to 100 yds for both conditions, effectively ignoring the zero point setting after that, and then directly comparing the predicted bullet drops at some longer distance such as 1000 yd. That is usually a very good illustration of how much less drag the bullet experiences during its flight at higher elevations.
CharlieNC
Gold $$ Contributor
Look closer at Strelok:
a. You can enable a feature whereby the envior conditions are used when zeroing vs assuming it is the same as shooting conditions. At 100 yards there is no effect, which is why this is typically chosen as the zero distance. There is no ballistic reason you should have observed a major shift.
b. It sounds like the calculation of 125fps slower is at the muzzle? That sounds like too much, as in Strelok has a built in default for the effect of temperature on muzzle velocity (due to powder sensitivity). Unless you know something, disable this by using the chart of velocity and temperature info as being the same.
Take the time to study ALL of the features of the ballistic calculator, as it is often a setup error/oversight that causes significant problems. But it continues to sound like you scope is shifting when traveling.
a. You can enable a feature whereby the envior conditions are used when zeroing vs assuming it is the same as shooting conditions. At 100 yards there is no effect, which is why this is typically chosen as the zero distance. There is no ballistic reason you should have observed a major shift.
b. It sounds like the calculation of 125fps slower is at the muzzle? That sounds like too much, as in Strelok has a built in default for the effect of temperature on muzzle velocity (due to powder sensitivity). Unless you know something, disable this by using the chart of velocity and temperature info as being the same.
Take the time to study ALL of the features of the ballistic calculator, as it is often a setup error/oversight that causes significant problems. But it continues to sound like you scope is shifting when traveling.
Quickload / Quicktarget I have been using for 20 years. It does a good job on elevation and temperature of the bullet travel. But for temp effects on the powder, I have to find the data and do my own estimates.
Because of that, the only powder I use that is not temp stable is CFE223, that gives me performance in short actions that offsets the temperature variation. I use IMR-4451 and IMR-4166 in long actions for the temp stability and non Copper fouling.
Because of that, the only powder I use that is not temp stable is CFE223, that gives me performance in short actions that offsets the temperature variation. I use IMR-4451 and IMR-4166 in long actions for the temp stability and non Copper fouling.
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