View Full Version : Adverse Heat Effect on Ammo question:

06-24-2010, 07:09 PM
I understand heat adversely impacts ammo.

I’m unsuccessful in finding any data on the topic other than heat + ammo= bad.

My ammo and reloading components are stored in a cool dry place.

The situation changes though when I have a range day after work, and my ammo sits in the back of my car all day.

Temperatures can get pretty high some times, and the ammo itself is hot to the touch and unpleasant to hold onto.

So I have gone to the trouble of getting a cooler w/cool pack to store my ammo in to prevent it from being exposed to heat or direct sunlight at the range and in my car for long periods of time.

The two big things I am trying to figure out are:
1) If exposed to heat what are the long term impacts? When I expose ammo to heat in the back of my car is the impact insignificant since I use the ammo shortly there after?
2) What is the performance level of ammo that was exposed to heat, and cooled down again and then shot relative to ammo that was never exposed to heat at all?
3) What is the difference of shooting currently hot ammo verses shooting cool ammo?

06-24-2010, 07:20 PM
Best answer I've found so far


Q. How long will ammunition last in storage?

A. Properly stored ammunition can last at least 40 years or more without any problems. However, the caveat here is "proper storage."

The method the military and ammunition industry use for long-term storage of ammunition is very old and very simple. Make a concrete bunker with walls about a foot thick. Then cover the whole thing about a yard deep with dirt. This construction is called an "igloo". The igloo produces a remarkably constancy in temperature and humidity inside, requiring neither power nor adjustment. Using this technique, modern small arms ammo may be stored for 40 or more years with no material degradation. Conversely, ammo "stored" in a hot car trunk may be dead as a mackerel, or wildly inconsistent in a single summer. However, not all of us have an "igloo" handy. Given even moderately consistent conditions most modern ammunition components are fairly resistant to degradation in the short run, say 10-15 years, absent high temperatures and/or constant temperature fluctuations.

To hit the high points of home storage very generally

1. In general, it is the PRIMER that you are worried about. Absent excessive high temperature and/or humidity, modern smokeless powder is very resistant to degradation in storage. As an interesting aside, corrosive priming compounds that use to be commonly in use have longer storage lives and are more resistant to degradation than comparable non-corrosive priming compounds.

2. No matter where you store ensure there is "dunnage" (i.e. 2x4 wood) under and between each layer stacked. Also ensure there is air space between stacked cases on the same layer. These provide air circulation which is crucial.

3. Humidity--Drier is better, but in sealed cans will make little difference if dunnage and air space are maintained. The ammunition should be packed with a desiccant. You can purchase a commercial product or go the "do-it-yourself" route. Go to any construction site and ask the straw boss if there are are any broken sheet rock boards around or some wallboard scraps. There will usually be. Sheet rock is gypsum and hydroscopic. Get a few pieces and cut them to about the size of a deck of cards square. Cook them in the oven at about 200 degrees for a few hours to drive the moisture out of them, then put one in each of your ammo cans. The piece will absorb what little moisture there may be in your ammo can, giving you a nice dry environment.

4. Temperature--This is a big one with lots of details. Good ammo is like good wine. Both like a constant, even temperature around 65 degrees F. The constancy of temperature is more important than the temperature itself. (This is a dandy excuse to build a wine cellar to store both.), And, as a wise man once said, "you can never have too much of either."

For short-term storage of general-usage ammunition, the most important factor is to keep the ammo out of excessive heat--say over 85 degrees. Excessive heat degrades ammunition. Ammo stored in car trunks is the most common victim here. Low temperatures do not harm ammunition per se. What degradation may occur is caused more by repeated temperature fluctuation than by the cold. (As an aside, double base powders can perform erratically when USED in very cold temperatures, but this is not a function of storage.)

At this point we probably should explain what we mean by "degradation" If you're storing MG ammo or "rattle battle" ammo, for a few years, the garage should suffice nicely, given the constraints above. The standard deviation of the velocity may go up slightly, but I suspect you will not notice a thing. On the other hand, if you are storing match ammunition, I'd recommend keeping the stuff in a place with a more even temperature. The bedroom closet, where the temperature stays nice all year, for instance. With something as precise as match ammunition even a little degradation could be of consequence.

Invest in a "min/max" thermometer that shows both the minimum and maximum temperature recorded. They run 10 bucks or so. Check your storage area monthly for signs of excessive temperature (check the min/max) or other degradation (rust on cans, etc.). There are no magic procedures. Just remember that equipment respected is equipment that will be reliable.

{As an example of what is possible, some years ago I fired some 60+ year old GI .45ACP ammo (FA 18 headstamp) that had been found in a military storage bunker. Of 40 rounds fired every one went off and 5 rounds over a chronograph averaged 788 f/s. -- FF}

Thanks to John Nichols for supplying this information--courtesy his stint with Uncle Sam.

To sum up.

Store ammunition and components in a temperature stable area (ideally 60 +/- 10 deg F)
Store in GI ammunition cans of good quality with good seals with a desiccant pack included
Have plenty of ventilation around the stored ammo cans and keep them off of floors.
If dampness my be present you can coat the ammo cans with liquid Alox to prevent long term rusting

Blackdog F4i
06-25-2010, 01:55 AM
The two big things I am trying to figure out are:
1) If exposed to heat what are the long term impacts? When I expose ammo to heat in the back of my car is the impact insignificant since I use the ammo shortly there after?

Yes, the impact is insignificant especially with pistol ammunition used at short ranges.

2) What is the performance level of ammo that was exposed to heat, and cooled down again and then shot relative to ammo that was never exposed to heat at all?

If it was only "heat cycled" a couple of times and shot within less than a year I will bet that it's indistinguishable from fresh ammo.

3) What is the difference of shooting currently hot ammo verses shooting cool ammo?

Depends. Hotter ammo will burn at a higher chamber pressure. With pistols at normal handgun range it's not generally something to worry about.

Now with a match grade high power rifle and match grade ammo you can see point of impact shifts from hot ammo. We always try to keep the ammo in the shade. However I just burned through 20 rounds of Federal Gold Metal Match that has been in my car in my callout bag for a year. It's been cooked and frozen numerous times. It still grouped right with the brand new box that I took out of my ammo storage in my climate controlled garage prior to heading to the range.

If it's match ammo, keep it in the shade and try not to let it cook in the chamber. If it's pistol or carbine ammo, screw it and burn it up.

06-25-2010, 01:10 PM
Living in the desert, when I go shooting in the summer most of my ammunition is pretty darn hot. I've never had any problems caused by it.

I do know that certain case/primer/powder combinations do not work well in very cold temperatures; sometimes all of the powder may not ignite if the weather is too cold.

06-25-2010, 03:19 PM
Thanks. Nothing to worry about, and I'll just shoot.

That's too bad. I had a not so great day at the range, and I was hoping to blame it on something :)

Blackdog F4i
06-25-2010, 03:37 PM
This is not directed at you so don't take it that way........

I tell guys that when I shoot I check my ego at the door. If I have a crappy day shooting I ask what did "I" do differently. When I have a really bad day I like to write in my logbook how I felt. Only after I take an honest look at myself, will I look at my equipment. Weak shooters frequently look for an excuse to their performance. Advanced shooters look for a reason and it's rarely in the equipment.

06-25-2010, 04:58 PM
Advanced shooters look for a reason and it's rarely in the equipment.

I had a rough session earlier this week with my 1947 Colt I got back from a gun smith.

I came to the conclusion this old Colt needed a new barrel, and since it wasn’t the original barrel to begin with I wasn’t lowering its value any.

Being aware I might be barking up the wrong tree in having work done on this old gun I tried to isolate the problems to the gun and not myself. So I brought the targets in to 10 and 15 yards, and compared my performance with it relative to another 1911 I have.

I figured at that range it should at least group decently, which it didn’t. It was also 3 inches up and 3 inches left POA, and I was threading a needle with my other 1911. If the POA wasn’t so off I would have left it, and just let it remain an Old Colt.

Fast forward, I finally got it back and it now has a Matched KART barrel and bushing. It’s basically now a sleeper GI model ;)

Over all, I was having a pretty shoddy performance with it the first time I took it out, but under those conditions the ammo was straight out of a hot car, and I also attributed the poor performance to the new barrel/ bushing break in.

Fast forward a little bit more to another range day with it I went to the trouble of letting the ammo cool down, and my performance improved.

My performance didn’t peak until I switched to 200g SWC bullets with 5.4g of Unique (verses 230g Ball with 5.7 of Unique). But by then the ammo was completely cooled off.

Sooooo, I’ll stop associating my improvement as a result of cooled down ammo, and associate it towards a lighter bullet with a lighter load which reduced the painful recoil effect as a result of no beaver tail on this old Colt.

I ended the day shooting my best (which is out of character) so I was looking for reasons why.

Conclusion: A GI model (i.e. non beaver tail) 1911 isn’t fun to shoot unless the ammo is light. If I am going to be shooting heavy load ammo out of a 1911 for any length of time it needs to have a beaver tail.

I can shoot 1.8 inch groups at 15 with my 1947 Colt and expect that to improve once I get more through it, but the catch is I can't be shooting 850 fps with 230g ball all day :D