I usually have a container in my vehicles with 100+ rounds of ammo of my 3 main calibers. It doesn't usually get shot up and is more for emergency need, so, what if any, is there any long term impact with temperature extremes from sitting is a vehicle for long periods of time. Time period extending beyond a year. Thoughts, background supporting info?

c4

Sample size of one. I kept a Sig SP2340 in 357 Sig loaded and stored in the back of Jeep Wrangler for 2 years in AZ. Was kept inside a zip lock bag stored inside small cordura backpack. Exposed directly to rain, snow and heat many times(the bag) both mags ran without issues(Win Ranger ammo)

I still carry guns in bags/cars but I've gotten in the habit of shooting through my carry ammo every 6 months or so.

I know this is apples to oranges but it’s a data point none the less.

I have shot WWI rifle ammo that most assuredly had seen damn near a century of temperature and moisture changes as well as the fact that my guess is modern ammo is made to a higher standard with better components.

With that in mind the most common failure I would see is a very short hang fire. CLICK......1 missisi BANG.

So my guess is your ammo will largely be fine.

What effects?
Does it matter if gunpowder in a handgun cartridge that will be used for a high speed engagement at 7 yards deteriorates to a degree and its performance is therefore changed to some small extent? How about if it’s ammunition for a precision rifle used to (try to) hit 12 inch plates at 1000 yards?

I have never seen any valid studies concerning the latter issue, but it’s a demonstrated fact that the temperature of ammunition can change its ballistics performance, so is it reasonable to believe that some changes can be permanent? Another thing we know is that ammunition manufacturers often caution that their products should be stored in cool environments; if there were no reason for that, why would they offer it?

Will ammunition that’s been stored under changing environmental conditions, including high temperatures, fire? Probably. I’ve fired rounds that I picked up from the range after being baked in the sun and frozen at below-zero temperatures for over a year, so, “It always went bang,” isn’t a definitive answer to the question unless going bang is the only thing we’re concerned about.

Seems if you have any concern over it (and I think it's valid to at least wonder) you'd make sure to cycle through it every six months or more often. I'm assuming it's 100 rounds of expensive JHP (assuming pistol rounds)? I'd probably do it this way:

Let's say one of the calibers in your car is 9mm, and you carry a P320 regularly and keep two 9mm magazines full, with 30 rounds. So every six months you buy 30 new rounds of 9mm JHP and replace in your two magazines of the gun you carry. Then you take the 30 rds you just removed from your carry rotation and put them in your car. You pull the rds that have been in your car for 6 months and shoot them next time you're at the range.

Personally, I think leaving guns and/or ammo in a vehicle permanently is irresponsible but maybe in your area things are different.

quote:

Originally posted by cobalt402:
I usually have a container in my vehicles with 100+ rounds of ammo of my 3 main calibers. It doesn't usually get shot up and is more for emergency need, so, what if any, is there any long term impact with temperature extremes from sitting is a vehicle for long periods of time. Time period extending beyond a year. Thoughts, background supporting info?

c4

I am interested in responses to this question as well. While I keep my “stockpile” in a temperature controlled and low humidity environment, it’s only because that is what my gun Mentor taught me. As for my practice ammo, I have never had a round age past a few months and empty my carry rounds down range every couple of months so no help from me on that part of your query.

On June 26, 1990 Phoenix hit 122 degrees, the hottest day on record (to date). I was working that day with about 1,000 rds of .45acp, 00 and 223 in the trunk of my assigned vehicle. No ill effects and most of it got shot before I retired years later.

You would think that over time some kind of change would occur in the propellant.
Without a controlled study of the chemical composition, pressure generated and velocity you have no way of knowing.

I've also shot some really old ammo and it seemed fine.
Just shooting it you're probably not going to tell the difference in 10, 20, even 50 feet per second.

quote:

Originally posted by az4783054:
On June 26, 1990 Phoenix hit 122 degrees, the hottest day on record (to date). I was working that day with about 1,000 rds of .45acp, 00 and 223 in the trunk of my assigned vehicle. No ill effects and most of it got shot before I retired years later.

And
And if it was 122F outside I would bet it was at least 140F-150F in the trunk of your assigned vehicle.....WOW....

Found this on the internet:

"Temperatures can become extreme in the winter and summer months and affect the nitrocellulose in your gun powder. If the temperature rises too high, your ammo can begin to sweat as the nitrocellulose inside starts to take a gas form.

Gas typically begins to seep out of your cartridge at 125 degrees Fahrenheit. This leakage can cause an imbalance inside your ammo changing the pressure in your firearm chamber. This can lead to significant inaccuracy upon firing. While the temperature outside may not reach that high, places like the inside of your vehicle have the potential to.

Reversely, freezing temperatures may not lead to a loss of powder in your cartridge, but it has a large possibility of changing the ballistic performance of your bullets. This can particularly affect the accuracy of shots fired with long-range rifle ammo."

https://ammunitionstore.com/pa...tices-dos-and-donts/

I have some 357 magnum ammo from when I went to college in 1964, it still shoots great. Stored in several garages over the years but still seems OK.

In 1970, I was stationed at Long Binh. It was the major supply depot for SE Asia. The average daily temp was over 100. There were thousands of TONS off all kinds of ammo stored there. It sat in the sun day after day. Some of it was even left over from WWII.

I never heard of any major problems.

A while back I came across some Remington 45ACP ammo my grandfather bought in 1916 for his Colt's Government model. In 1917 he loaded a bunch of it it into 12 Colt's brand magazines when he was preparing to go off to WWI. The gun and magazines were prepared for my grandmother to use if necessary (it turned out to be smart as she did need them.) In 1918 she used two magazines on a home invader.

The remaining magazines came to me after he died some years ago.

I had to try some of the old ammo... in fact it was over 90 years old when I tried it out...

The result: The ammo shot just fine and the magazines worked without problems as well.

The ammo was stored for at least 50 years in un air conditioned houses in the humidity of South Louisiana.

My judgement is heat may cause some minor changes in performance, but the changes are minimal...

FWIW...

Chuck...

Oh, forgot to add I shot quite a lot of 30-40 US 'tin can' ammo in the early 1970s that had 1899 head stamps... also with no problems except it was corrosive so it required a lot of cleaning.

I can answer to what I have found. We used at my agency new reloaded .40 ammo from Ga Arms for practice for about 10 years. I found a full box that was behind the spare tire of a spare patrol car from 1994 in the year 2006. I know because I had placed it in the car. So for about 12 years it was hot and cold Georgia weather give or take 20f to 130f. during this time. When fired from the 60 yard line it would not strike the target. From the 25 yard line it struck about 3 inches from point of aim. So based on that non scientific test I tell folks rotate ammo once a year and shoot for practice what you replace. I myself no longer leave more that one box of ammunition in a patrol car or my personal cars anymore...VI

Heat is the major killer of ammunition.

But, it must be taken with a grain of salt.

We used to track the ammo temps on big gun cartridges because when it was fired the hot temps actually affected the range of the round, same as cold ammo..the military figured this out in the end of the 1800s and started keeping logs of ammo and it’s fall of shot and concluded some things.

WRT small arms ammo..I don’t worry about ammo left in a car. Ever.

Heat does affect pyrotechnics adversely very quickly, but pyro is only changed out of life rafts when the rafts are scheduled to be inspected...IIRC every four years....we replaced the pyro and burned the old stuff for training ASAP. It sometimes did wonky things like the smoke would burn vs smoking...flares burnt like they were supposed to.

I shot ammo for 20mm cannons from 1938...in 1992...nary a problem.

I qualified with 45ACP in 1988 with ammo from the 40’s...still worked and god only knows where it was kept.

We used grenade cartridges from the 30’s for our line throwing gun in 2000....and it was blackpowder...

I only shoot my carry ammo annually so that I can buy new stuff, mainly because I might chamber and re chamber it occasionally and I don’t want a round with set-back in my duty carry. So I shoot it yearly.

I keep two full mags of ball 9mm in my truck for just in case for my Glock and I have never had a problem with it firing...I might remember to shoot it with my edc ammo or I might forget...I’m not worried about it.

Handgun and rifle ammo stored in the same temperatures and humidity levels humans like is typically good for many, many decades. Five easily, 10 quite possibly. High temperatures and humidity could cut that by 60%.

Shotgun ammo, not so much, as the Plastic case could deteriorate after several years in even temperature and humidity controlled environment.

If you’re not able to properly store and rotate ammo for many years, you may need to have a much larger inventory. 10,000 rounds of each caliber you run with is a good inventory level for most people.

Other than the heat, would having ammo stored in a vehicle be affected by the constant jarring and shaking over the course of thousands of miles? Primer compounds being shaken loose?

I don't think that is anything you need to worry about.

quote:

Originally posted by Nismo:
Other than the heat, would having ammo stored in a vehicle be affected by the constant jarring and shaking over the course of thousands of miles? Primer compounds being shaken loose?

quote:

Originally posted by Nismo:
[W]ould having ammo stored in a vehicle be affected by the constant jarring and shaking over the course of thousands of miles?

That’s another question that has been raised by the pundits over the years, but I haven’t seen any references to it recently. The concern was that as loose powder is continually shaken inside a cartridge case the individual grains can be physically broken into to smaller pieces. That would be most likely with extruded powders made into longer tubes rather than flake or ball powder. If the granules are broken that would change their burning characteristics and possibly their ballistic performance. Whether that would be a valid concern I don’t know myself, and I haven’t seen any discussion of the issue in many years.

Anyone who is seriously interested in the subject should keep two things in mind. The first is to compare apples to apples. There are countless different types of propellants and explosives, and if we’re concerned about smokeless gunpowder that’s what we should be looking at, not other things that go bang.

The second, and to reiterate, is that if going bang is all we’re concerned about, storage conditions will matter far less than if we’re trying to get first round hits at 1000 yards with a precision rifle. For the latter it’s well known among precision shooters that even the temperature of the ammunition when it’s fired can affect its ballistics. That fact is recognized to the point that efforts have been made to produce powder that is minimally sensitive to temperature changes.
Can anything else that affects the powder’s physical or chemical properties also have an effect? Perhaps not, but I certainly wouldn’t bet the rent on such an assumption. For 99+% of shooters ammunition storage conditions are probably immaterial, but just because most of us can’t see an effect doesn’t mean it doesn’t exist.

I rotate out all the ammo in our patrol cars once a year. Same with my personal car.