Thread: Effects of cartridge temp on velocity

From Strelok
Altitude 0', temp 60F, the difference between 990HPa and 1030HPa is +0.2 MOA (11.26 vs 11.46 MOA) at 600 yards for my 7RM, so approximately 1.2". Significant?
If you zeroed at standard pressure (1013.25 HPa) you would likely only get a +/- half inch variation at that distance.

Originally Posted by Shearer

From Strelok
Altitude 0', temp 60F, the difference between 990HPa and 1030HPa is +0.2 MOA (11.26 vs 11.46 MOA) at 600 yards for my 7RM, so approximately 1.2". Significant?
If you zeroed at standard pressure (1013.25 HPa) you would likely only get a +/- half inch variation at that distance.

Good stuff. I couldnt remember how much but knew there was a difference.

1.2" might not mean much on a bit of steel or kill zone of an animal but if you are already on the edge because of other factors it could save you if allowed for.

So aside from the nut behind the butt and bad reloads we are back to temp as being the most influential atmospheric factor.




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Be interesting to see how stable you find the old W760 when you take a few extra notes Dave.

I agree. Best to mitigate any variable we do have control over but to me, the single biggest variable on POI when shooting at distance is wind. And this is not something we can measure accurately like we can temperature, pressure, altitude or distance.
We know what it is doing where we are (we can measure it there) and we can judge fairly accurately what it is doing at out target through environmental factors (trees/grasses blowing etc) but we can only guess what it is doing in between us and our target. Also wind is three dimensional. Not only does it blow from side to side, it blows up and down, and towards and away from us.
Imagine shooting across a gully with a steady 15kph wind from left to right. We allow for that but there may well be a 3kph overall up draft and a 5kph tail wind in the middle of the valley we are not aware of so can make no allowance for. Both will have a bigger effect on POI than a moderate change in air pressure.
Having done a bit of flying @R93 you will be well aware of the surprises and unpredictability of the wind in the mountains. It is a very rare day when there is no air movement at all.

Originally Posted by Mathias

Be interesting to see how stable you find the old W760 when you take a few extra notes Dave.

So far so good. But yeah. Haven't really tested with the 760 for ES during the warmer months.

I don't generally use my .260 in the spring or summer other than to shoot a bit of steel for fun.

I no longer shoot long range as far as animals go, simply because I have got away without any screw ups as far as the shooting goes.

The .223 does 99% of the freezer filling.

But my interest in medium to LR shooting steel or paper and everything that goes with it, is still pretty high.


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Originally Posted by Shearer

I agree. Best to mitigate any variable we do have control over but to me, the single biggest variable on POI when shooting at distance is wind. And this is not something we can measure accurately like we can temperature, pressure, altitude or distance.
We know what it is doing where we are (we can measure it there) and we can judge fairly accurately what it is doing at out target through environmental factors (trees/grasses blowing etc) but we can only guess what it is doing in between us and our target. Also wind is three dimensional. Not only does it blow from side to side, it blows up and down, and towards and away from us.
Imagine shooting across a gully with a steady 15kph wind from left to right. We allow for that but there may well be a 3kph overall up draft and a 5kph tail wind in the middle of the valley we are not aware of so can make no allowance for. Both will have a bigger effect on POI than a moderate change in air pressure.
Having done a bit of flying @R93 you will be well aware of the surprises and unpredictability of the wind in the mountains. It is a very rare day when there is no air movement at all.

I did forget wind all be it intentionally and agree it is the biggest atmospheric factor. Poor choice of words before.

I am more interested in what I can maybe control with knowledge and experimentation.



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I've never noticed a difference at hunting ranges @R93 but mainly use Adi powder as it's the most temp stable.
At longer range 1500+ the difference in summer is huge especially if your ammo box is in the sun, we negate this buy using a chilly bag, not so much to chill the ammo but keep the temperature controlled.
I've seen some nasty results with N560 that got to hot.
Interesting thread.

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I loved N560 for my 6.5-06 And a mates .280 AI
I thought it had a tendency to spike more so than a temp problem?

I have an sort of insulated pouch for my hunting ammo. Holds around 8 rnds.

I might see if using that makes a difference in any way opposed to just picking rounds from a container off the shooting bench.



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Originally Posted by R93

My interest in medium to LR shooting steel or paper and everything that goes with it, is still pretty high.

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I built my 260Imp with the same thought in mind. I wouldn't be keen to use past 500m on game due to my limited current LR ability and it wouldn't sit with me ethically anyway out past that. Paper & steel past this....yes please, anytime.

Balistic AE has an option in reload data to allow for fps/ deg change. I find it works well. Its been a slow process to identify reliably, hoping the Labradar will speed this up a bit. I make sure the rifle is at the ambient temp as well as the ammo.
As with most things the range is relevant but more so the total elevation needed.

I use shooter and strelok. Shooter just works and is easier for me to use.

It has an input for powder temp and I have tried to find info on it but not with much luck.

I always enter the daily temp and that could be an issue as the ammo is unlikely to be the same. Especially after being in a pouch, pocket on pack or chambered for a while etc.
I have a laser thermometer but not sure how accurate it is. But it may add a control measure for a test. Spose it's better than tormenting the cooks cat with it

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Once its established you dont have to enter it again, it just works of the atmo.
Excluding altitude,atmospheric change seems to cancel itself out in many situations as higher pressure usually comes with warmer temps leveling out air density change

Originally Posted by sneeze

Once its established you dont have to enter it again, it just works of the atmo.
Excluding altitude,atmospheric change seems to cancel itself out in many situations as higher pressure usually comes with warmer temps leveling out air density change

Are you talking about Powder temp?
If so how do establish it accurately on the first place?

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I am sure I have seen a chart of various powders and velocity results per temp somewhere.
All I remember of it was some powders actually lost velocity as temp was raised for a start....IE for some powders it is not a linear relationship.

Originally Posted by R93

Are you talking about Powder temp?
If so how do establish it accurately on the first place?

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Yes basically, Powder sensitivity to temp change . I shot it over a range ambient temps at long range. So 243ai out to 800 yds and work the velocity back from the drop. then calculate the difference in fps per deg of temp change. A lot of variables so iv tried to get as big a sample as possible. Yet to do it with the 338 but hoping the ease of use and inherent accuracy of the labradr will make it a lot simpler.
I prefer everthing to be at the temp I'm testing , ammo gun and atomos so I dont just chill down the ammo in the ice box and shoot them on a hot day so its a slow process.