I will be hunting very soon where the temperature will be 100 degrees F, plus or minus.

Where I live, it is very cold this time of year. The temperature is generally below freezing and today will be -15 degrees F.

I have sighted in my rifle and I'm happy with how and where it is shooting.

But this has got me thinking. I've never been very far off in temperature between home and where I'll be hunting - nowhere near the delta of between 80-100 degrees F that I'm expecting this time.

Has anyone experienced this kind of temperature difference under similar circumstances?

I wonder if there will be any significant change in POI when shooting in such radically different climates.

Mike,

It is normal to check your rifle zero at camp.

In my own experiment, I found no change.

My shooting room is air conditioned and the temperature is around 22.

I loaded ammo for my 375/404 and put them in the sun in August.

Temperatures almost 50.

The cartridges are practically too hot to handle.

I ran down and shot them.

I shot others left in the room.

I think I shot 6 rounds.

3 hot and 3 normal.

I did not see any difference.

That is a great experiment and test, Saeed. I could probably do something like it.

I would have to keep my rifle and ammo warm inside the truck at the range, then hustle to the firing line and shoot three rounds fairly quickly while all was still warm.

Then stand by for a while and let the rifle and ammo cool to ambient, below freezing temperature and try again.

If I can find the time, I think I'll do that and see if I replicate your results.

I will, of course, check my zero in camp, but I do hate wasting ammo!

Mike
I just finished hunting in Uganda, temp was 85 to 90 F. I was shooting my guns at home temp was 20F. I didn’t have any noticeable shift at 100 yds when checking both guns
Craig

I have not personally noticed a noticeable change when using loads developed in Michigan and checking zeros in Texas. With this said I know of two people that have had problems with increased pressures in hot zones.
The first was with a person who is no longer with us, but was using factory loads in Africa hunting dangerous game and shot a civet cat on the way back from a days hunt. His action locked up after the shot and had to be banged open. Previous shots did not have any issues. Lucky for him he was not shooting at anything requiring a follow up shot. Who knows if it was a bad load or if the load was close to pressure maximum and the extra temperature put it over the edge.
The second was with a friend that I shoot bench rest competition with. His load was developed during colder months. During an afternoon match he had issues with higher pressures and one round popping a primer. To solve this problem on the second day the ammunition was stored in a cooler containing ice. Not an option during a hunt. These loads were ok at lower temperature, but excessive at higher temperatures.
I would expect with higher temperatures come higher pressures and theoretically the bullet strike will be higher. By how much I don’t know. I would recheck your zero once you get to your camp, and if you load your own stay well below maximum loads or try to develop loads on a hot day at home. Perhaps you try keeping your ammo in a warm cooler when you zero your rifle to minimize differences.
I wonder if someone with quick load could run the program same loads comparing zero and one hundred degrees to see the difference in velocity. Your rifle will probably be a big variable and predicting impact change could only be confirmed by actual shooting.
Disclaimer – I have only been to Africa once and my experience level is probably much less than the average person posting here.

Well, probably not. Temperature can have at least three major effects. First, if your barrel is not free-floated, or is marginally so, differential thermal expansion can cause pressure on the barrel and change POI. If you haven't noticed this before, you're probably OK and as mentioned, you should confirm zero in camp.

Temperature will affect powder burn rates and muzzle velocity. For hunting at 0-400 yards this is trivial, but one does have to consider this for very long range shooting (1000 yards+). Different powders vary in this regard. H4350 likely has the least temperature sensitivity and is prized by 6.5 Creedmoor long-range shooters for this reason.

However, this temperature sensitivity can also affect chamber pressure. A load that is safe and functions reliably at sub-zero temperatures can potentially be overpressure and result in the case sticking in the chamber when fired at high ambient temperatures, especially if multiple rounds are fired.

Thanks, all, for your thoughts.

I'm not worried about high pressure in the heat since I've hunted in very hot conditions with the same ammunition I'll be using this time around. Never had any problems.

It's only the potential for a change in POI that is making me curious.

a lot depends on what powder is used. Some powders are more sensitive to temp than others. I have the exact opposite situation. I usually develop my loads during the summer when it is 80 and hunt in the fall when it can be below zero. I have noticed a 200 fps drop in velocity with some powders with a big temp change down. Mostly with some of the ball powders. Most of the modern powders are way less sensitive.

Mike,
As a competitive rifle shooter, temp sensitivity can be a concern, but normally only at longer ranges, think 600+ yards and beyond. Some powders are more sensitive to changes in temperatures, but most are not. At normal hunting ranges I think it would have to be a serious change in chamber pressures to show much difference 300 yards and closer.
John

Michael.

It is never a waste of ammo to check zero and adjust if necessary.

I think the main reason for changes in zero due to climate differences is due to humidity and wood stocks. I switched to synthetic stocks on my main hunting rifles a number of years ago, but then again, there isn't a whole lot of difference in temperatures or humidity between Texas and the hottest places I've hunted in Africa.

quote:

I would have to keep my rifle and ammo warm inside the truck at the range,

Seeing you are at 0 or sub-zero temps. if you want to simulate near-African temps. keep your desired number of target ammo under the hood with engine running at the range.

Density altitude does play a role in ballistics. A pretty minor one though that is covered by checking zero in camp. Ambient temp, altitude, and humidity figure into the equation. Checking zero at camp does it without a table.

My biggest POA shift was... me... going from -30F here to 100+F in Cameroon, I was not seeing things well, I was not shooting well, and I was absolutely unacclimated. Yes, it got better as time went on, but my Savanna hunt in Cameroon was probably some of the worst shooting that I have ever done, personally.

Yesterday, Not Very Far From My Home!

I am looking forward to warmer and sunnier climes.

One must be brain dead to live in cold places!

Yesterday in the desert, temperature was 11 C.

Got out of the car barefoot as usual!

My toes froze up!

Had to get back in and put the heater on!

No wonder humans originated in Africa!

quote:

Originally posted by Michael Robinson:
Yesterday, Not Very Far From My Home!

I am looking forward to warmer and sunnier climes.

Mike, i am positive you were not out shooting on such a windy day.

I believe that elevation will play a bigger point of impact on your rifle than cool and warm weather.

So have you checked to see what your elevation difference will be?

And for such an important hunt, if you were that concerned about your point of impact change relative to temperature differences, you would have made a quick trip to Florida, Texas or Arizona and double checked your rifle’s point of impact.

quote:

Originally posted by Saeed:
One must be brain dead to live in cold places!

Yesterday in the desert, temperature was 11 C.

Got out of the car barefoot as usual!

My toes froze up!

Had to get back in and put the heater on!

No wonder humans originated in Africa!

Saeed, you could do the same with snow, you need to try the bare foot in fresh snow, then flop down and give your best try for a snow angel. Then run for your warm vehicle to warm up, refreshing is all one can say.

I find the difference between American and African gun writers interesting: Americans focus on loading for more speed and Africans seem focused on pressure. Stories about frozen actions and dangerous game would explain the difference.

quote:

Originally posted by Saeed:
One must be brain dead to live in cold places!

I was thinking exactly the same thing while at the range just the other day!

Trying to hold off into a 20 mph cross-wind at 0 degrees F will do that to you.

Just kidding. Not even I am that brain dead.

The weather is supposed to warm up this week.

Good guides and good hunters, check their rifles zero in camp before they start the hunt. Every hunter should demand that.

quote:

Originally posted by Saeed:
One must be brain dead to live in cold places!

Yesterday in the desert, temperature was 11 C.

Got out of the car barefoot as usual!

My toes froze up!

Had to get back in and put the heater on!

No wonder humans originated in Africa!

I live in a place that has a very large temperature range. It can get up to the high 90's in the summer and -50 in the winter. What I find amazing is how well the human body can climatize to the temps. A couple weeks or so at a temp range is enough to work. After a couple of weeks when the temps are in the 90's I am comfortable and feel cold at 60. The flip side is also true. A couple weeks at -20 and I can run around in a tee shirt when the temp gets to 40.

I am way more comfortable in cold weather than hot. I would have a tough time living in a hot desert enviroment.

quote:

Originally posted by Atkinson:
Good guides and good hunters, check their rifles zero in camp before they start the hunt. Every hunter should demand that.

And often the scope needs tuning

They will have a target set up for you to shoot. It wasn't very far. Maybe 75 meters.

I know nothings about the technical details . However , I went from Florida where the temperature was in the mid 80’s to Tajikistan where it was minus 15. It was not a problem.

A lot of the IMR powders being of ancient formulation are temperature sensitive. Other brands not so much.