Ammo in HOT cars. Okay, but seems it wouldn't be.

[Orion8472]

I'm curious about something. I heard that it can't get hot enough in a car to "cook off" the ammo in your gun, when it is sitting in your car, and the temps are close to 100F. But I touched the metal part of my shifter and really couldn't do it for more than 8 seconds before it was too hot to the touch. So, I got thinking about the ammo as it would be just as hot as the metal part of the shifter.

Does it matter what type of ammo? Would 22lr be more apt to "cook off" than centerfire ammo?

 

[NIGHTLORD40K]

"Cook off? No- but high temps will cause smokeless powder to degrade, and become less stable, faster, though we are talking about long-term exposure and it wouldnt actually become dangerously unstable for years even so.

A bigger issue is probably humidity seeping into the cartridge cases, contaminating the powder and primers and causing case corrosion. Since rimfire cases are generally not sealed as well as centerfire- and the primers tend to fall apart when subjected to vibration such as road travel- I would surmise that .22LR would be more severely affected.

Now, would I keep surplus WW2 Japanese Nambu ammo in a hot car........uh, no.

Bottom line, its a good idea to rotate any ammo that is regularly exposed to heat and humidity to limit its exposure.

 

[Orion8472]

I see. A most, my gun would only be in my car through the work day on a Friday.

 

[Hartkopf]

It takes 350 degrees to cook off ammo IIRC.

 

[BigAlShooter]

A vehicle in the hottest environment can reach 185F inside, but that is very rare, maybe 135F on the dash on the hottest day here in Georgia. I work in the automotive industry and we test to these extremes on all parts.
But, your ammo is safe.
We've all seen people (or fools) punish their guns by shooting them until the barrel is red hot. I'd assume the ammo, if sat in the barrel for long, would cook off, but it never does, as it takes a while for all of the components of the ammo to heat up. The gun just keeps firing without a hiccup. Just think of all those machine guns in all of the wars, where they change out barrels and have to soak them in water as they are blazing hot. But, they shoot the ammo too fast for it to heat up.
I would suggest that the smaller the ammo, the more it may heat up faster. But, still probably not an issue.

 

[jmr40]

If you were allow the ammo to reach 135 degrees, and fire it at that temp you could have an over pressure round. Especially with loads near the max. Most ammo is tested at about 70 degrees to get the numbers you see in ballistics charts. You can expect 1-2 fps velocity change for each 1 degree of temperature change. So at 0 degrees you could be 70-140 fps slower than normal. At 140 degrees 70-140 fps faster than normal.

The above data is for rifle rounds. Temperature effects handgun ammo too, but I haven't seen any data specifically for handguns so it might not exactly the same.

 

[Orion8472]

BigAlShooter, that is a really good point...about ammo sitting in a red hot barrel.

As a side note, on the topic of new cars and HOT days,...those with the screens, how do they keep them from getting hot and frying? I would think that those screens would not do well in the very hot temps.

 

[FROGO207]

The temps to cook off ammo would be a good bit above the melting point of the standard plastics used in a car. You never see any melted plastic parts do you. Any ammo I leave in my vehicle for a season turns into range ammo to practice with what I carry. Then I rotate in new for the next summer season. Never had any problems but do not shoot them in 100* + weather either.

 

[.38 Special]

Decades ago some gunwriter wrote up an incident where he'd left a box of rifle cartridges on his dashboard and when he fired the hot-to-the-touch rounds they printed shockingly high. Obviously in that situation they were generating more than the usual pressure, and after the remainder had cooled off they went back to their normal point of impact. Many of today's powders are supposedly more temperature stable, but in extreme scenarios, who knows.

Beyond that, if the inside of your car is so hot that your ammo is cooking off, you've got bigger problems!

 

[Howland937]

2 things I know.

#1, my Cherokee hasn't had a/c in over 10 years and the better part of 300k miles, so whatever the temp is outside it's the same (or hotter) inside.
#2, ammo I found under the back seat (deer slugs, circa 2010 and 10-15 .22's) fired just fine last fall. Thats a lot of heating/cooling cycles in 10 summers.

 

[627PCFan]

Food for thought. Your car's interior might hit 140 degrees in the afternoon in August but usually, your console typically is substantially cooler in temperature.

 

[BigAlShooter]

Orion, those displays are made a little different than your tv display. Basically, they use better adhesives and have special bonding and laminating processes. Those displays and touchscreens are basically many layers bonded to a glass layer. And then we validate the crap out of them. Thermal shock +85C to -20C in quick cycles for 1,000's of cycles. I wonder if any ammo manufacturers test their ammo in any temperature validation tests? I'd assume all ammo material's are "about" the same, meaning the primer material and base materials of the powder and brass is the same content, so if one will pass a test, they all should be similar.

 

[AK Hunter]

2 things I know.

#1, my Cherokee hasn't had a/c in over 10 years and the better part of 300k miles, so whatever the temp is outside it's the same inside.
#2, ammo I found under the back seat (deer slugs, circa 2010 and 10-15 .22's) fired just fine last fall. Thats a lot of heating/cooling cycles in 10 summers.

I bought an old 4x4 from a buddy to use as a hunting truck. He had used it for about the same thing. His hunting slugs would get pitched on the dash when he cleared his gun. The slug round would drop down the defrost vents as he drove. I drove it for a few years then the blower motor went out. As I changed the blower motor I saw the blockage in the defroster vents & removed it. There is no telling how many hot cold cycles these rounds went through but they all shot fine & were accurate.

 

[Speedo66]

2 things I know.

#1, my Cherokee hasn't had a/c in over 10 years and the better part of 300k miles, so whatever the temp is outside it's the same inside.

I think with all the glass it creates a greenhouse effect, so temp inside can easily exceed the outside temp, just like a greenhouse does in winter.

My extreme experience with a hot car: Got into a Subaru parked all day in a hot NYC area, because I was soaked in sweat so bad I didn't want to blast A/C directly on me. The A/C in that Imprezza was cold enough to hang meat.

I turned the vents away from me, straight up, and promptly had a crack line expanding through the windshield. You could actually hear it as it traveled.

As far as ammo, I've had some in broiling hot attics, damp basements, garages in a variety of temps, and they all went bang.

 

[SquidBubble]

Ambient temperature would have to be somewhere around 350 to 400 degrees to cook your ammo to the point of ignition. You could park your vehicle in Death Valley, engine running and heater on full blast with the windows up, and inside temps will still never got hot enough for ammo to light off on its own.

 

[Orion8472]

BigAlShooter, thanks for the reply on the automotive screens. It's just been something I've wondered about since, in computers, heat kills them.

Yeah, I also wonder if any testing has been done,...but from what I'm getting from you and others, it appears to be not an issue for ammo in a summer hot car. I appreciate all the replies!

BTW,....SquidBubble,.......the avatar.........OMG!!

 

[JohnKSa]

It gets pretty hot in TX in the car after it's been sitting in a huge asphalt lot for hours when the outside temps get over 100. Hot enough to heat-deform some plastics.

The ammo does not cook off. I accept that the heat will degrade it over time, but I can tell you from experience that even after being in the car for an entire summer it still shoots fine and (at least without a chronograph) there is no detectable change in performance.

 

[bullseye308]

Just think of all the ammo in the Middle East sitting in conex boxes waiting to be used by our soldiers. Think of all the bouncing around in the heat that ammo is subjected to, and how well it still performs. If you are still worried about your ammo, replace it twice a year with fresh ammo and you will be fine. I leave a couple extra Glock mags in my Explorer year round with no AC and rolled up windows unless I’m driving. I’ve never had a problem in many years of doing it. I rotate it out at least once a year, and have never had a round fail.

 

[milemaker13]

Rounds in red hot barrels not good for several reasons. This is why MGs and SMGs fire from open bolts.

 

[CapnMac]

There's a parallel for this in that most attics in CONUS can get up to 130-140ºF for periods of 3 to 12 hours at a time.
This makes attics particularly bad places for long-term ammo storage.

The Code required attic ventilation is the residential equivalent of lowering your auto windows from 1/2 to 1 inch; good for 5-10ºF of cooling (attic or car are the same).

The windshield screens work by reflecting the heat back out of the car, before it gets absorbed by the various interior "bits" of the auto.

 

[George P]

And it can get that hot over in that war-torn sandbox and the ammo works.

 

[danez71]

BigAlShooter, thanks for the reply on the automotive screens. It's just been something I've wondered about since, in computers, heat kills them

Not to digress,
Typically for electronics...
Commercial grade = 0 to +70C
Industrial = -40 to +85C
Automotive can be = -40 to +105C or -40 to +125C
Military is usually -55 to +125C or sometimes 150C.

I believe those are all operating temps. Junction temps are about another 15-25C higher.

It gets pretty hot in TX in the car after it's been sitting in a huge asphalt lot for hours when the outside temps get over 100. Hot enough to heat-deform some plastics.

To that point,
In AZ, it was 122F on truck thermometer that reads outside air temp and 123 on bank thermometer I had just passed by.

I stopped to pick up a pizza I had preordered. I left the truck running and ran inside. Literally 2-3 minutes max and the truck temp said 136 when I got back. It was an asphalt parking lot. Another time the thermometer just had a " - " so I know the air temp was hotter than 136. I was parked on concrete in front of a metal roll up garage door for maybe an hour - 90 min.

I got over 160 using an inferred thermometer on my dash and steering wheel when I tried it once. Back in the day, cassette tapes were no match.

Ammo wasn't ever noticeably affected, though.

 

[Howland937]

I think with all the glass it creates a greenhouse effect, so temp inside can easily exceed the outside temp, just like a greenhouse does in winter

True...it definitely gets hotter inside if I roll the windows up. I kinda forgot since I only put them up if it's raining.

 

[Tirod]

"Cook off? No- but high temps will cause smokeless powder to degrade, and become less stable, faster, though we are talking about long-term exposure and it wouldnt actually become dangerously unstable for years even so.

A bigger issue is probably humidity seeping into the cartridge cases, contaminating the powder and primers and causing case corrosion. Since rimfire cases are generally not sealed as well as centerfire- and the primers tend to fall apart when subjected to vibration such as road travel- I would surmise that .22LR would be more severely affected.

Now, would I keep surplus WW2 Japanese Nambu ammo in a hot car........uh, no.

Bottom line, its a good idea to rotate any ammo that is regularly exposed to heat and humidity to limit its exposure.

FPNI.

Cars have been monitored and will exceed 160F in worst case conditions. They will kill small children and pets if left inside unattended. As for storage, the real issue is the accumulation of humidity, which will condense on colder metallic objects. That means your cold metal gun parts will get water from the air collecting on them, which includes cartridge cases made of metal. Including the one in the chamber. That water will creep between the case and chamber wall, and because of the imbalance of electrical charge set up electrolytic corrosion. You could just as easily dip the gun in water once a week and leave it in the trunk to dry out.

Polymer won't, altho 160F and long term exposure will cause deformation of fiberglass reinforced nylon, and those of us who remember the black toolboxes in pickup trucks thru the 80's also remember them bowing under the weight of tools when left out in summer temps. A lot got propped up with concrete blocks, seemed to be about the right height. Along with the heat problem was the gasketing to keep out water, which always fails as the box settles, and it allows humid air to infiltrate, getting tools soaking wet and even pooling up in the bottom. Worst cases I've seen are 4-6 inches of water sloshing around. Trunks, too.

But, it's ok to keep a gun in there. And guns have ammo. It's a recipe for disaster. And we haven't even addressed how many guns are stolen from parked cars, many times right in front of a home. Yet we ridicule the idea that stolen guns are what are sold in Detroit and keeping the murder rate so high, yet organize and debate why law enforcement shouldn't trace stolen guns and penalize the insecure and lazy storage.

Guns in cars corrode, rust, cartridges fail, and they get stolen which supports crime and murder. Not much good to the owner long term, carry is your better option.

 

[edwardware]

I heard that it can't get hot enough in a car to "cook off" the ammo in your gun. . .

Yes, you can.

Of course, all of the plastic in your car would be puddled in the floor pan, so you wouldn't mind the damage at the point.

Recall that lots of ammo our military uses overseas got there in a shipping container, and likely sat in the sun in Saudi for a year before being opened. You'll be fine just rotating your carry ammo once a year.