Yes, ammunition will go off in a fire. Most small arms propellants ignite at roughly 350 to 450 degrees Fahrenheit, a temperature that a house fire reaches within minutes. But what happens next is very different from what most people picture. Loose ammunition cooking off in a fire is far less dangerous than a bullet fired from a gun, though the real risks depend heavily on how and where the ammo is stored.
What Temperature Sets It Off
The propellant inside a cartridge is primarily nitrated cellulose, which has an autoignition temperature similar to paper. If you’ve heard of the novel “Fahrenheit 451,” that title refers to paper’s ignition point, and ammunition propellant falls in the same neighborhood. Most rounds will cook off somewhere between 350 and 450 degrees Fahrenheit.
Well before that point, heat starts doing damage. Propellant begins to chemically degrade at temperatures above 180°F, which can make rounds unstable or unreliable even if they don’t ignite. In a structure fire, where temperatures commonly exceed 1,000°F in upper layers of a room, any exposed ammunition will eventually reach ignition temperature.
Why Loose Rounds Are Less Dangerous Than You Think
When a round fires inside a gun, the chamber seals around the cartridge and directs all that expanding gas in one direction: behind the bullet. The bullet accelerates down the barrel and exits at high velocity. Without a chamber, the physics change completely.
A cartridge that ignites in the open has nothing containing the pressure. The brass or steel casing, being lighter and weaker than the bullet in most calibers, simply bursts. The bullet, which is the heavier component, tends to barely move from where it sat. Think of it less like a gunshot and more like a loud firecracker. The energy disperses in all directions instead of being focused behind the projectile, so the bullet pops out of the case at extremely low velocity.
Small fragments of the burst casing and primer cup can be thrown short distances, typically no more than 50 feet, at speeds that could cause minor injury or discomfort to unprotected skin. But standard firefighter turnout gear is enough to stop these fragments. For this reason, fire service guidance generally treats loose, unchambered small arms ammunition as a nuisance rather than a serious ballistic threat.
How Storage Containers Change the Risk
The container your ammunition sits in during a fire makes a significant difference in how dangerous the situation becomes.
Ammunition in factory cardboard boxes behaves much like loose rounds. The cardboard offers no containment, so each round that ignites just pops and bursts in place. There’s a small hazard in the immediate area, but no bullets flying at meaningful speed.
Metal ammo cans are a different story. Many gun owners store ammunition in surplus military cans with latching lids, and these create a sealed, confined space. When rounds start cooking off inside a sealed metal container, the pressure builds with nowhere to go. The result is closer to a pipe bomb than a string of firecrackers. The can itself can rupture violently, sending metal fragments outward with real force. This is one of the more counterintuitive storage risks: the container people choose for organization and moisture protection actually increases the danger during a fire.
A fire-resistant safe is the recommended middle ground. A quality safe slows heat transfer, buying time before rounds reach ignition temperature. If rounds do eventually cook off inside, the safe’s heavy walls can often contain the pressure and fragments, reducing the hazard for anyone nearby or for responding firefighters.
Ammunition Loaded in Firearms Is the Biggest Danger
The most dangerous scenario in a fire is ammunition that’s chambered in a firearm. A round sitting in a gun’s chamber has exactly the confinement it needs to function like a normal shot. When heat causes the primer or propellant to ignite, the bullet can travel down the barrel at or near its designed velocity.
This isn’t just theoretical. In fire investigations, semi-automatic firearms have been documented cycling through multiple rounds as heat caused each chambered cartridge to fire, with the recoil and gas system feeding the next round into the chamber. A loaded gun in a house fire can effectively fire itself, with bullets capable of penetrating walls and injuring people outside the structure. Firefighters consistently rank loaded firearms as the most serious ammunition-related hazard they face.
Toxic Smoke Is an Overlooked Hazard
Beyond the explosion risk, burning ammunition releases toxic fumes that most people don’t consider. Bullet projectiles are predominantly lead, and the primer compound in each cartridge contains roughly 35% lead styphnate and lead peroxide, along with barium and antimony compounds. When these materials burn, they produce fine lead particulates and chemical fumes.
Under normal firing conditions at a gun range, these lead particles are already a recognized health concern for shooters who inhale them. In a fire, where dozens or hundreds of rounds may cook off in an enclosed space, the concentration of lead dust and heavy metal fumes in the smoke and residue can be substantial. Anyone near the fire without respiratory protection faces potential inhalation exposure. This is worth knowing if you’re ever in a situation where ammunition has burned in a garage, basement, or vehicle: treat the residue and lingering dust as a lead contamination concern, not just ordinary fire debris.
Practical Takeaways for Storage
If you store ammunition at home, a few choices reduce fire risk meaningfully. Keep ammo in a fire-rated safe rather than in sealed metal cans. If a safe isn’t practical, factory cardboard boxes or open containers are actually safer than sealed metal ones, since they allow pressure to vent rather than build. Store ammunition separately from firearms when possible, and avoid leaving rounds chambered in guns that are stored long-term. Keep your ammunition storage area away from heat sources, flammable liquids, and areas where a fire is most likely to start, like kitchens, furnace rooms, and garages with fuel or solvents.
If you ever need to alert firefighters that ammunition is inside a burning structure, tell them. Knowing the location, approximate quantity, and whether any loaded firearms are present helps them assess the risk and choose their approach. Loose boxed ammo in a back bedroom is a very different situation from a sealed ammo can next to a loaded rifle.