The idea of a bullet “exploding” like a firework when exposed to fire is a common misconception, often fueled by dramatic portrayals in movies. While a cartridge will react to high temperatures, the actual event is far less explosive than typically depicted. The reality is more nuanced and still potentially dangerous.
How a Cartridge Reacts to Fire
A complete cartridge consists of several components: the projectile (the actual bullet), a casing, propellant (gunpowder), and a primer. When subjected to intense heat, such as in a fire, heat transfers to the primer. This primer contains a sensitive chemical mixture designed to ignite with impact or sufficient heat.
Once the primer ignites, it produces a small flash of flame. This flash then ignites the main propellant charge within the casing. Modern propellants burn rapidly, generating a large volume of hot gases and pressure inside the cartridge casing.
In a firearm, the rigid walls of the gun barrel and chamber confine this rapidly expanding gas, directing pressure to propel the bullet forward at high velocity. Without this confinement, the pressure has no single direction to escape. The casing becomes the weakest point and will rupture or split, releasing the gas and expelling the projectile and/or casing fragments in an unpredictable manner. The projectile typically travels only a few feet with very low velocity, as the energy is not efficiently directed into its movement. The casing, being lighter, may travel further than the bullet.
Real Dangers and Common Misconceptions
While a cartridge’s reaction in a fire is not a cinematic explosion, it still presents real hazards. The uncontrolled expulsion of the projectile or casing fragments can cause serious injury, including burns from hot metal, cuts from shrapnel, or impact wounds. The direction of travel for both the bullet and casing fragments is unpredictable, meaning anyone nearby could be at risk.
The primary danger comes from the unpredictable scattering of hot metal, not from a high-velocity projectile as if fired from a gun. Numerous tests demonstrate that loose ammunition in a fire does not pose the same threat as ammunition discharged from a firearm. The idea that bullets will “whiz dangerously about” with significant force or cause a chain reaction is a common misconception. Attempting to throw cartridges into a fire is extremely dangerous and should never be attempted.