I've been storing all my primers in a those sealed green military surplus ammo cans along with desiccant cartridges.  I figured what better way to prevent moisture & humidity from degrading them.  I was curious & asked Googles AI how to properly store primers.  

Wayne

Here's the response:

Ideal Storage Conditions
•      Cool temperatures: Maintain a stable environment between 50°F and 70°F.
•      Low humidity: Keep relative humidity around 60% or lower.
•      Original packaging: Leave primers in their original plastic trays and cardboard sleeves.
•      No metal containers: Avoid storing primers in sealed metal boxes or ammunition cans.
•      Ventilation: Use storage cabinets designed to vent pressure safely in an accidental fire.

So, I then asked, why no metal containers & got this response:

Storing primers in a sealed metal container turns a fire hazard into an explosion hazard.
Pressure and Fragmentation Hazards
•      Pressure Containment: Metal containers are often designed to be airtight and structurally robust. While this protects the contents from moisture, it also allows for a significant build-up of internal pressure in the event of a fire.
•      Rapid Expansion: If the primers are exposed to extreme heat, they will undergo a rapid chemical reaction. In a confined space, the resulting gases expand faster than the container can vent.
•      Structural Failure: The sealed metal container will contain the pressure until its structural limits are exceeded, leading to a violent rupture.
•      Fragmentation: During such a rupture, the metal walls of the container can break apart into high-velocity fragments, creating a significant hazard to anyone nearby and potentially damaging the surrounding structure.

George Babits wrote on Aug 28^th, 2026 at 4:02pm:


George, you're just smarter than me.  It's common knowledge for storing powder.  I never considered it for primers.

Wayne

Never heard of a building designed with walls to blow in.

I used to shoot highpower at the Nebraska National Guard range. It was located on the old arsenal from WWII were bombs were made. The buildings were brick structures but the sides were about 4 courses of brick then 8’-10’ of glass windows then 4 courses of brick then the roof.  I was told that if something blew they could save the building.

I understand the idea that storing primers in a strong enclosed box such as an ammo can  could result in an explosion when the combined pressure of the detonating primers exceeds the strength of the ammo can. Would that same concept not apply to storing loaded ammunition in an ammo can? A cartridge that detonates outside a gun chamber would not create the pressure that would result in a locked chamber, but if you had several hundred cartridges cooking off in an ammo can would you not have the same problem?  I hope there is an explanation for this because I have lots of loaded ammo stored in ammo cans!
Seemed like such a good idea at the time!

Joe S.

As a former Combat Engineer and a shooter since 1960, here are a couple thoughts. First, smokeless powder is a propellant, it's not an explosive. Even if a respectable quantity was ignited in a sealed ammo can, the can will only resist the pressure until the lid fails. Remember GIGO, with computers? The AI quoted is garbage. AI is saying a metal can will resist long enough to make the powder go high order, the "explosion" will be violent enough to actually produce shrapnel. Impossible.The flame front in an initiator, a high explosive, moves at or greater than the speed of sound. Rifle and pistol propellants are much slower than that. High order is analogous to high explosive. It begins with civilian dynamite and proceeds on up to C4, gelignite, etc. The resistance posed by a can is not going to make the propellant explode. You have to confine it. That's why experimenters and terrorists use heavy pipe to make bombs. As to primers, they're different. The lead styphnate in our primers is an explosive. A quantity ignited will explode on its own, it doesn't need to be confined like rifle propellants. Storing it maybe 1,000 at a time and separated is the way I like to do it. The NRA and their researchers, H.P. White Laboratories in Bel Air, Md. researched powders and their behavior in fires, etc. many years ago. They proved the movie images of ammunition stored in a house that's burning being lethal is baloney. The bullet in a cartridge will come out of the case with a mild pop and that's it. It's not confined. Powder however IS a hazard in such a fire, as a simple flammable.

a number of years back, out in the boonies of Nevada, a friend and I came across the leavings of an accidental (?) fire in a pickup that had been left abandoned. Big fire, seemingly began in the engine compartment and spread till the camper on it had been burnt out as well- leaving much inside damaged and in ruin. We searched it for 'goodies' and found a very few. I found a new shovel a few yards away, cast in frustration I assume upon failing to extinguish the blaze. Inside, Steve found a .44 mag round and handed it to me as he kept seeking the gun it was for. Nope, not there. I had my second interesting prize. That pistol cartridge was lacking its primer, and the jacket for the bullet was still seated, though the exposed lead had melted away. 
So, it made me wholly convince that fire isn't gonna cause much violent bursting of a common cartridge such as we all use. It's a neat sample in my collection of oddball ammo.

JoeS
The reason for the 1" wood lining for my 20 mm ammo cans
is Thermal Insulation during a possible fire in my "cave" that would extend the time for the contents to get up to ignition temperature.
The national fire regulations do refer to fire resistant containers
for flamables,etc. I have one that we constructed for in the Lab
I ran to hold flammable solvents, etc. It now resides in my garage.
They specify nominal 1" wood construction throughout.
I just carried the idea "into" my 20mm ammo cans for storing powder beyond the capacity of the fire resistant cabinet in the garage. I also built another 1" walled wood box to fit my
20# DuPont 4227 and 12# 4759 kegs.
beltfed/arnie