The flash hole
is the part of a cartridge
that is the circular opening at the bottom of the case and is where the primer
jets out the flame
and hot gases when it is struck by the firing pin
In Boxer primed ammo there is only one flash hole as compared to Berdan Primed ammo that usually has two smaller flash holes.
Primer powered ammunition usually have enlarged flash holes as it is only the ignition of the primer that is used to propel the light projectile. Cases modified for this function should no longer be reloaded to fire full charge service ammunition.