Relating this
testing to "Real" Cartridges
An interesting and important characteristic
of the 44 Magnum tests and the Inert-Only test in the 45-70 is that
primer residues extended full length of case interior and onto bullet
base. This deposition diminished from base of case, toward base of
bullet. It was obviously concentrated on simulant located near primer
and on case walls near web. This deposit on case interior wall showed
obvious indications that granules in contact with case walls had moved
forward after initial primer residue deposition. This, "scraping"
of primer residues on case walls was concentrated near a point about
1/3-inch forward of case web and diminished progressively toward bullet
base.
Besides being interesting in its own right, evidence that primer blast significantly compresses simulant (by driving base of charge toward bullet) may help us solve another aspect of internal ballistics that this simple inert-under-propellant test cannot resolve, specifically: in a normal smokeless load, in addition to percentage of propellant charge directly ignited by primer, how much additional propellant is ignited by gases from nascent propellant ignition before significant bullet movement occurs?
Ample evidence from theoretical considerations and from various types of testing suggests that such nascent ignition gas derived from propellant cannot reach particularly far into initially unignited propellant for two reasons. First, momentum transfer from primer blast, along with pressure build up toward rear of propellant column from primer gases and nascent granule ignition, works to rapidly and significantly compress forward portion of charge. This