Summer vs Winter velocities and temp stability

[Greg S]

10" @ 500 is only 2" @ 100 or with IMR powder 20°.

 

[Xmark1]

Yes, understanding this POI difference is the goal. I also need to track POI shift with elevation changes but its rare I get to target shoot in another part of the state but eventually will take a trip.

I live here in Portland, and I shoot mostly within a 75-mile radius of the city. But the things I have learned about differing temperatures can be applied anywhere. I also own property in N. Washington and sometimes shoot in Bend. Both of these places get colder than Portland.
Long ago I started keeping a detailed logbook for each firearm I shoot. I made notes about where I was shooting, elevation, temperature, different hand loads, distance, wind, and much more. This habit has served me well.
Memories fade but notes don't lie.
When I started seeing things like changes in POI from when I started shooting midday to perhaps seven - or ten-degrees cooler as evening approached, it was a real eye opener! I am now so familiar with this phenomenon that as the day cools, I automatically increase my elevation dope. This is especially apparent when shooting 300+ yards. But since I shoot out to a mile (about 1,760 yards) it is a need-to-know skill.
Before I learned these things, I would pull my hair out wondering why my POI kept changing!
Perhaps I should note for newbies that this phenomenon is most apparent once you get past, say 250 yards.
My $.02

 

[Xmark1]

10" @ 500 is only 2" @ 100 or with IMR powder 20°.

The POI decay is not linear. It's more exponential as projectile velocity decreases with yardage. And the colder it is, the denser the air is, and velocity decreases faster with yardage.
I know that different powders react differently to ambient temperature. However, the things I speak of apply to a known (chrono-graphed) MV at the current known temperature.
I use a 100 yard zero with my 308.

 

[dangerranger60]

The first I heard of Vihtavouri powders was how temp stable they were.
I live where it gets hot and stays hot! It can get over 150 degrees in a closed up car left in the sun.
So a friend that shoots Silhouettes was the first to jump on the new temp stable powder. He worked up a new load during the fall and tested it through the winter. the next spring there had been no real change until the first match in the heat. In the morning he checked his drops and everything was fine but his group did not shoot till after lunch. By that time it was 105 degrees. at that temp he had trouble opening the bolt, problems ejecting etc...
We decided that his powder was temp stable to cold, not so much to the heat.

 

[Mono1]

I live here in Portland, and I shoot mostly within a 75-mile radius of the city. But the things I have learned about differing temperatures can be applied anywhere. I also own property in N. Washington and sometimes shoot in Bend. Both of these places get colder than Portland.
Long ago I started keeping a detailed logbook for each firearm I shoot. I made notes about where I was shooting, elevation, temperature, different hand loads, distance, wind, and much more. This habit has served me well.
Memories fade but notes don't lie.
When I started seeing things like changes in POI from when I started shooting midday to perhaps seven - or ten-degrees cooler as evening approached, it was a real eye opener! I am now so familiar with this phenomenon that as the day cools, I automatically increase my elevation dope. This is especially apparent when shooting 400+ yards. But since I shoot out to a mile (about 1,760 yards) it is a need-to-know skill.
Before I learned these things, I would pull my hair out wondering why my POI kept changing!
Perhaps I should note for newbies that this phenomenon is most apparent once you get past, say 250 yards.
My $.02

Hey @Xmark1 please excuse the dumb questions, but firstly I assume the 10 inch POI difference you mentioned earlier is entirely vertical (elevation) correct? Also, is the higher POI in summer? Thanks so much! Old Guy, but still learning here.

 

[Mono1]

10" @ 500 is only 2" @ 100

For the Accuracy-Analists here (such as I) 2 MOA is heart-breaking!

 

[Spitpatch]

Holy Crap! That is a Big Difference!

I was not aware of that. Thanks for the education!

Gosh. The quite occasional unpredictables of long-range shooting. They are incalculable in number and rate.

Intriguing and amusing, A parlor game, which when applied to a living animal as a test subject is obscenity at its worst.

...But an admirable pursuit of valid achievement on the target field.

 

[Mono1]

Gosh. The quite occasional unpredictables of long-range shooting. They are incalculable in number and rate.

Intriguing and amusing, A parlor game, which when applied to a living animal as a test subject is obscenity at its worst.

...But an admirable pursuit of valid achievement on the target field.

DAM, Spit.

Thats Poetic.

 

[Koda]

Hopefully nobodys suggesting to long range hunt, but I remember years ago my first lesson in temperature was I took my hunting rifle out one summer to shoot it and the POI was off maybe 2inches from my zero. Baffled me for a while but when I learned it was a summer temperature effect I simply started checking my rifle zero the week before opening day and it was back on. Never gave it much thought after that until recently learning to handload.

Back in 2022 the deer season was incredibly unseasonably hot for over half the season, then it rained the last 3 weeks... I'm sure the temperature difference was great. Hunters that only use one rifle that hunt both deer and elk can easily find huge temp (and altitude) differences between seasons, so powder sensitivity is important for hunters to be aware of too.

 

[Xaevian]

I prefer Hodgdon extreme powders. Temp ranges for me are -20 to 105F. I would rather not have an overpressure on the hottest day or a big POI shift at 300+ yards on a game animal when it is well below zero, 6000+ feet elevation, windy, and it hurts to breathe.

Of course, my rifles are for killing things, not competition and I don't really shoot past 300 yds, so that is the perspective I have. I also don't sight my rifles in when it is over 70 out (50-60 would be ideal IMO). I won't mess with the scopes if I am just slinging lead for fun when it is 90+ degrees in the shade, but I don't really see much of a POI shift at hunting distance anyway.

That is just me, though. I'm no Chris Kyle, but I have a 90% overall success rate hunting the last 20 years with only 1 miss last year (that was a different issue, not powder related but still stupid) and just 12 hunting hours in with no animal this year.

 

[P7M13]

so powder sensitivity is important for hunters to be aware of too.

Yes and no. Like you, I find Butterbean's chart on LRH to be interesting but wonder at its source.
As @Xmark1 noted, observation recorded in dope books is invaluable.
Hence, I don't worry too much about temp sensitivity, as a lot of the powders I load with are temp sensitive.
With today's prices and past scarcity, I work with what I have on hand. Beggars can't be choosers.
What I want to know, and take notes on, is what my loading will shoot out of my rifle under what conditions.

 

[Xmark1]

Hey @Xmark1 please excuse the dumb questions, but firstly I assume the 10 inch POI difference you mentioned earlier is entirely vertical (elevation) correct? Also, is the higher POI in summer? Thanks so much! Old Guy, but still learning here.

Ha-ha. I had to read that twice as it's a trick question.

Let us assume you zeroed your rifle @ 87 degrees ambient temp in the summer. 100 yard zero, no wind.

So, if you use the same rifle that was doped for a 100 yard zero in the summer, in winter ---
Cold air is denser therefore it slows the projectile down faster than warm air. So, the winter POI will be lower. The elevation dope will need to be adjusted higher.
The change applies to elevation only, windage is a different subject. Let's assume for the sake of argument there is no wind. Then there is no effect on windage.

If there is wind, it will have a more powerful effect on your projectiles flight path because cold air is denser.
Personally, I dope elevation for a given temp/yardage with my turrets, but I correct for windage on the fly because the wind is constantly changing.

 

[Xmark1]

Yes and no. Like you, I find Butterbean's chart on LRH to be interesting but wonder at its source.
As @Xmark1 noted, observation recorded in dope books is invaluable.
Hence, I don't worry too much about temp sensitivity, as a lot of the powders I load with are temp sensitive.
With today's prices and past scarcity, I work with what I have on hand. Beggars can't be choosers.
What I want to know, and take notes on, is what my loading will shoot out of my rifle under what conditions.

Gosh. The quite occasional unpredictables of long-range shooting. They are incalculable in number and rate.

Intriguing and amusing, A parlor game, which when applied to a living animal as a test subject is obscenity at its worst.

...But an admirable pursuit of valid achievement on the target field.

I seldom shoot at an animal out past 300 yards, but that's usually because this old fart can't see farther than that without glass.
Hell, countless times I have been standing no more than 20-30 yards from a buck and did not see it until it bolted.

 

[Koda]

Yes and no. Like you, I find Butterbean's chart on LRH to be interesting but wonder at its source.

I should add to my statement that (for better or worse) there is a growing trend in long range hunting and for anyone who shoots over 300yds at game I think should be aware of the temperature stability of their load.

 

[Mono1]

Ha-ha. I had to read that twice as it's a trick question.

Let us assume you zeroed your rifle @ 87 degrees ambient temp in the summer. 100 yard zero, no wind.

So, if you use the same rifle that was doped for a 100 yard zero in the summer, in winter ---
Cold air is denser therefore it slows the projectile down faster than warm air. So, the winter POI will be lower. The elevation dope will need to be adjusted higher.
The change applies to elevation only, windage is a different subject. Let's assume for the sake of argument there is no wind. Then there is no effect on windage.

If there is wind, it will have a more powerful effect on your projectiles flight path because cold air is denser.
Personally, I dope elevation for a given temp/yardage with my turrets, but I correct for windage on the fly because the wind is constantly changing.

Thank You Bro.

 

[orygun]

Once I was going to see what high temps would do to the cartridges, so I left 5 on the dash of the truck on a sunny day. I forgot them until I'd packed everything away...
I use RL22, which isn't supposed to be all that temp stable. I do most of my load development in the summer when it's fun to be out in the woods. I always recheck zero shortly before deer season when the temps are a little lower. 20-30 degree reduction, no difference. Once when we went elk hunting we needed to sight in my wife's rifle at camp. I tool the opportunity to check mine, too. 2000' more elevation and almost 50 degrees less temp and I put bullets in the same place as at "home". (all of this at 100 yards)
I do not hunt "long range". In fact, I've never even shot at a deer or elk past 70-75 yards.
Within the typical (for me) distances I shoot at, I've never been able to tell the difference when the temp is anywhere from the 20's to the 90's. If I had the place to consistently shoot at 400 yards it would be a much better test of this phenomenon.

Maybe RL22 isn't all that bad?

 

[Koda]

Once I was going to see what high temps would do to the cartridges, so I left 5 on the dash of the truck on a sunny day. I forgot them until I'd packed everything away...
I use RL22, which isn't supposed to be all that temp stable. I do most of my load development in the summer when it's fun to be out in the woods. I always recheck zero shortly before deer season when the temps are a little lower. 20-30 degree reduction, no difference. Once when we went elk hunting we needed to sight in my wife's rifle at camp. I tool the opportunity to check mine, too. 2000' more elevation and almost 50 degrees less temp and I put bullets in the same place as at "home". (all of this at 100 yards)
I do not hunt "long range". In fact, I've never even shot at a deer or elk past 70-75 yards.
Within the typical (for me) distances I shoot at, I've never been able to tell the difference when the temp is anywhere from the 20's to the 90's. If I had the place to consistently shoot at 400 yards it would be a much better test of this phenomenon.

Maybe RL22 isn't all that bad?

I haven't used RL22 but at the range your hunting you'd probably never notice. My guess is at 100yds, you'd have to shoot from a benchrest to notice any temp difference affecting POI.
I doubt RL22 is "that" unstable that out in the woods over a backpack or whatever it would be noticeable at 100yds.

If you ever felt like experimenting, RL23 is supposed to be the temp stable version of RL22, it might be an easy swap in the recipe though I would run a pressure ladder to be sure.

 

[orygun]

I haven't used RL22 but at the range your hunting you'd probably never notice. My guess is at 100yds, you'd have to shoot from a benchrest to notice any temp difference affecting POI.
I doubt RL22 is "that" unstable that out in the woods over a backpack or whatever it would be noticeable at 100yds.

If you ever felt like experimenting, RL23 is supposed to be the temp stable version of RL22, it might be an easy swap in the recipe though I would run a pressure ladder to be sure.

If I wasn't sitting on 7 or 8 pounds of RL22, I would try RL23. At the rate I'm going thru it, I have 10 lifetimes of it left! I have a great, accurate load for my Ackley (30-06) and will load up a bunch after I get the press mounted back up. But as soon as I can get back to loading, it's 257 Roberts time! I've not worked with a "new" cartridge since I started loading for the Ackley 5 or 6 years ago.

 

[Koda]

If I wasn't sitting on 7 or 8 pounds of RL22, I would try RL23. At the rate I'm going thru it, I have 10 lifetimes of it left! I have a great, accurate load for my Ackley (30-06) and will load up a bunch after I get the press mounted back up. But as soon as I can get back to loading, it's 257 Roberts time! I've not worked with a "new" cartridge since I started loading for the Ackley 5 or 6 years ago.

I wouldnt change a thing then, I know what its like to invest in a supply of powder... eventually you have to use what you got. The RL22 might even work in your 257 Roberts with the heavier bullets.

 

[orygun]

I wouldnt change a thing then, I know what its like to invest in a supply of powder... eventually you have to use what you got. The RL22 might even work in your 257 Roberts with the heavier bullets.

Maybe, but in this case I am going to take the advice of a very seasoned shooter/reloader and start with 4350.