Effects of cartridge temp on velocity

Before I start, it pays to note that the following dribble will not have much relevance to anyone that shoots normal hunting ranges and doesn't suffer OCD regarding, reloading.
Hopefully there may be something useful to some.


With the rifle calibers that I use, I have been trying to find a happy medium regarding temperature when doing load development. For accuracy at distance and most importantly safety.

My experience is that there is a small but notable difference in velocity of said loads between summer and winter.
This would be common knowledge to anyone into reloading and shooting.
Could be useful for those not aware and might be right on, or over a max load that has been developed during the winter months.

The velocity difference, varies slightly between the calibers I shoot. Mostly .223 and .260.

The .223 will differ on average 85fps on a common day between both seasons where as my .260 has a 60fps avg difference.

Reading a bit of guff on the subject the consensus thru some pretty stringent testing is that for every 1 degree change in Fahrenheit (1° C is 33.8 ° F) regarding cartridge temp, there is a gain or loss of 1.5 fps. This if right, would be dependant on a few variables.

So that's saying every 1°C the velocity should increase or decrease 50.7 fps?

So where I live the coast the average temp shift at sea level, between the seasons of say mid winter to mid summer, is around 15°C with an extreme day here and there.

In saying that, if cartridge temp is close to outside temp, a load doing 2950 fps on a 11°C day in the winter should increase by around 700fps on a summers day of 25°C to 3650 fps.!
That is if I have understood what I have read right.

Something has to be way off in those estimates, even with some other cartridge dynamics aside.

From my notes and in my rifle over the last few years the change between say 11 degrees and 25 degrees, the velocity difference observed is under 100 fps.

What I have applied from this is to do all my load development, or at least confirm all load development in the summer.

I then halve the difference in velocity that I have observed between seasons and have made a summer and winter profile on my ballistic calculator. I make sure I zero and input those atmospherics on an average day for those seasons.

This in turn has made a notable improvement in my expected POI when shooting at steel between 5 and 700. (As far as I have tested so far)

I used to get a 6-7 inch vertical differences on first shots and have till recently, put up with it.

Since applying my new data the vertical difference I have observed, so far, is now well under half that.












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Not quite Dave, 11 celsius = 51.8F 25 celsius = 77F so only a 25.2 F change x 1.5 = 37.8 fps change.

The celsius to fahrenheit conversion is not constant across the temperature range -40C and -40F are the same temp

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Originally Posted by stug

Not quite Dave, 11 celsius = 51.8F 25 celsius = 77F so only a 25.2 F change x 1.5 = 37.8 fps change.

The celsius to fahrenheit conversion is not constant across the temperature range -40C and -40F are the same temp

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Yeah uncle googled fucked me when I looked it up.
Thanks for that. Makes it all fall into line and realistic now.



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That's very good, intense, work @R93, with editing by @stug. The importance of observation and range notes, yes? And thorough research. Well done and thankyou. Will apply it to my own reloading. :thumbsup: But not so sure 40C and 40f are equal! Might need to check again, Stug ;)

okay, right, @stug, just observed the - . Didn't see it through the flyshit on my screen. Apologies.

It also depends on what powder you are using some are more temperature sensitive than others, some of the US long range shooters keep their ammo in a cooler bag/bin
to keep the temperature even through out the shoot, I have done it when shooting F class on a hot day don't know if it helped but it didn't hurt

Basically 9/5 conversion C to F, and 5/9 from F to C for degrees change.

So each degree C change will be 9/5 * 1.5 = 2.7fps/C

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Originally Posted by shooternz

It also depends on what powder you are using some are more temperature sensitive than others, some of the US long range shooters keep their ammo in a cooler bag/bin
to keep the temperature even through out the shoot, I have done it when shooting F class on a hot day don't know if it helped but it didn't hurt

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Thanks for mentioning that mate.[emoji106]

They were the next things I was going to explore. Powder and powder types.

And secondly if there was anything you could do too lessen the effect, by way of ammo storage on your person or in a piece of equipment like a cooler etc.

I have held a number of rounds in my pocket during the winter for a test.
Tried with both .223 and .260

Fired them over a v3 and the ES was all over the place compared to the same loaded batch of ammo I had on the bench.
Was an eye opener and sort of what led me down this path of thinking and testing.


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Greg Duley did a powder temperature comparison a few years back. Some powders were definitly worse than others.

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Originally Posted by stug

Greg Duley did a powder temperature comparison a few years back. Some powders were definitly worse than others.

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And yet some of those powders that have a bad name regarding temp, work really well for some over long term use and different batches.

RL 17 comes to mind. It was one of the most consistent I have used for one of my barrels but you could never get it when you wanted it[emoji14]

If I see more than a few bad reports on a powder I will generally avoid it tho.



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How about this, how does the air pressure effect the muzzle velocity? Does it have any effect. My first thought is that a lower air pressure (higher air temp) would give a higher muzzle velocity because there is less resistance in front of the projectile in the barrel. Or is it such a small factor the friction between projectile and barrel negate it?

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Originally Posted by stug

How about this, how does the air pressure effect the muzzle velocity? Does it have any effect. My first thought is that a lower air pressure (higher air temp) would give a higher muzzle velocity because there is less resistance in front of the projectile in the barrel. Or is it such a small factor the friction between projectile and barrel negate it?

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Not sure if it effects muzzle velocity too much but higher and lower pressures effect POI at distance.

You can see it on a ballistic calc with a 10 or 20 mb change.
So my dumb logic says the denser the air the faster the projectile loses velocity And vice versa?







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Yep agree with you there Dave about the effect of air pressure on the trajectory. Just wondering if some of the muzzle velocity increase at higher temp is also coming from the redcution in air pressure that comes with higher temp. Have you recorded pressure values along with temperature and muzzle velocity? @Norway might have an idea.

To convert temperatures in degrees Celsius to Fahrenheit, multiply by 1.8 (or 9/5) and add 32. (must add the 32)

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Originally Posted by stug

Yep agree with you there Dave about the effect of air pressure on the trajectory. Just wondering if some of the muzzle velocity increase at higher temp is also coming from the redcution in air pressure that comes with higher temp. Have you recorded pressure values along with temperature and muzzle velocity? @Norway might have an idea.

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Lately I have been recording everything.
But I have not got that info on me here in PNG.

In summer at home you can get a 27°day with 1028-1030mb
With the orographic lifting you can have a 27° day with 990-low 1000mb.

I have noted a difference for said range and what I have had to dial.
Just can't remember if it was much but there is a difference.

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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.

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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.

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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.[emoji6]

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.

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Originally Posted by Mathias

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

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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.

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I did forget wind all be it intentionally and agree it is the biggest atmospheric factor. Poor choice of words before. [emoji14]

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[emoji14]

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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

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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

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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.

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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.

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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

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Frosty mornings being the exception to that.

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Originally Posted by Shearer

Frosty mornings being the exception to that.

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Yes thats why I said "many situations" not All.

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Originally Posted by stug

How about this, how does the air pressure effect the muzzle velocity? Does it have any effect. My first thought is that a lower air pressure (higher air temp) would give a higher muzzle velocity because there is less resistance in front of the projectile in the barrel. Or is it such a small factor the friction between projectile and barrel negate it?

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I read just yesterday on a US forum a guy tested this. His smith built his rifle and testfired it at sea level, the rifle and remainder of the box of ammo was then shipped it to him, he lives at 4000 feet and when he tested the left over ammo he got the same velocity as the smith.

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Originally Posted by wsm junkie

I read just yesterday on a US forum a guy tested this. His smith built his rifle and testfired it at sea level, the rifle and remainder of the box of ammo was then shipped it to him, he lives at 4000 feet and when he tested the left over ammo he got the same velocity as the smith.

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Altitude simply effects air density. So does temperature. Temperature normally decreases with altitude (the amount varies depending on humidity) so they were probably shooting in the same "thickness" of air.

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Originally Posted by Shearer

Altitude simply effects air density. So does temperature. Temperature normally decreases with altitude (the amount varies depending on humidity) so they were probably shooting in the same "thickness" of air.

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Dont forget air pressure lapses with altitude as well at a given rate per 100ft.

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Originally Posted by R93

Dont forget air pressure lapses with altitude as well at a given rate per 100ft.

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Yeah. That's what I am thinking. As the altitude increases the pressure decreases (because of reducing air density) but the temperature also decreases (increasing air density) but not necessarily at the same rate.
Please let a scientist clarify this before I talk myself into a hole.
In the example given, air will cool between 1.5 and 3 degrees /1000' of altitude (depending on it's saturation level), so a rise of 4000" altitude will equate to a temperature drop of between 6 and 12 degrees Celsius.

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Originally Posted by Shearer

Yeah. That's what I am thinking. As the altitude increases the pressure decreases (because of reducing air density) but the temperature also decreases (increasing air density) but not necessarily at the same rate.
Please let a scientist clarify this before I talk myself into a hole.
In the example given, air will cool between 1.5 and 3 degrees /1000' of altitude, so a rise of 4000" altitude will equate to a temperature drop of between 6 and 12 degrees Celsius.

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Ha Ha you did alright. I passed my met exam that was full of all that stuff a while ago. I can't remember we the formula as I just went off QNH or dialed my know altitude on the altimeter[emoji38]

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Being a sample size of one, shot on different days by different shooters with unknown chronys or method of measurement Id say its a conclusion of very limited value.

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Originally Posted by sneeze

Being a sample size of one, shot on different days by different shooters with unknown chronys or method of measurement Id say its a conclusion of very limited value.

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Yeah. Not a lot of detail.

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Originally Posted by Shearer

Yeah. That's what I am thinking. As the altitude increases the pressure decreases (because of reducing air density) but the temperature also decreases (increasing air density) but not necessarily at the same rate.
Please let a scientist clarify this before I talk myself into a hole.
In the example given, air will cool between 1.5 and 3 degrees /1000' of altitude, so a rise of 4000" altitude will equate to a temperature drop of between 6 and 12 degrees Celsius.

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The main thing, I think, is that the lower temperature reduces MV. This largely offsets the lower pressure/air density so the trajectory is much the same.