As far as spontaneous combustion of the priming compound is concerned, the flameless ignition temperature of small arms priming compounds is generally in the region of 190-260 °C. This is considerably lower than the ignition temperature for most small arms propellants, which is in the region of 350 °C. It can be assumed, therefore, that during a fire, the first thing to spontaneously ignite will be the primer which will, in turn, ignite the propellant.
Such ignitions are virtually harmless as the soft brass case of the round and the lightly held bullet in the case mouth do not allow the pressures to build up sufficiently for the case to explode. At most, the case wall will rupture, with no more than the odd piece of brass being projected a few feet and the primer being pushed out of its pocket.
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