How Granules Ignite and how Granules Contribute to Bullet
Velocity For simplicity sake, we will consider these basic types of
granule ignition (for a typical rifle cartridge):
1. Super Ignited:
Granules proximal to flash hole shattered by primer blast – this material
ignites and burns many times faster than unbroken granules and hence,
when considered on a grain-for-grain basis, it contributes greatest
energy to bullet acceleration. Note that such pulverization may not
occur to any granules, whether or not this happens depends upon granule
toughness (granule composition, configuration, shape, and temperature);
primer brisance, flash hole diameter and configuration; and charge
density.
2. Primary Ignition: Granules having essentially 100% of surface
area heated to, or beyond, ignition temperature by primer plume and
hence contributing almost as much bullet energy as super ignited granules.
3.
Partial Primary Ignition: Granules having some portion of surface
area heated to, or beyond, ignition point temperature by primer plume
and that will therefore contribute almost as much bullet energy as
do primarily ignited granules.
4. Secondary Ignition: Granules that
primer plume does not heat sufficiently on any portion of surface
to achieve ignition but which are subsequently heated sufficiently
by nascent granule combustion to begin burning (through radiant and
conductive heating), before bullet has moved more than, perhaps, 15%
of distance toward muzzle; such granules can contribute significant
energy to bullet acceleration (how much contribution any such granule
can make depends upon