base of the lead bullet was noted to have been impressed with the shape of the propellant granules. This test was repeated with less inert simulant and more live propellant in five-grain increments until ignition occurred. The height of the inert propellant column was then measured at 0.6 inches. This test was repeated with several different live propellants and primers. All ignitions occurred between 0.5 and 0.6 inch inert column height. It is interesting to note that magnum rifle primers gave ignitions tending toward 0.5 inches and weaker primers such as the match type tended toward 0.6 inches. This is believed to have been caused by the higher pressures generated by the magnum primers closing off more of the interstitial air gaps.
Generation Of
Shear Lines In Gun Cartridges
Use of the generated shear line areas
to predict gun cartridge peak pressures and other aspects of cartridge
performance has not been previously disclosed or utilized. This is
therefore considered an advancement of the state of the art.
Cartridges which have internal lengths measured from flash hole to bullet base less than 0.6 inches in general do not have a discernable shear line formed behind the bullet because nearly all propellant is ignited by the primer. Thus cartridge configurations described by Alexander, Patent #6293203 B1 are excluded. (Most pistol propellants have compressions in excess of 20% at first bullet movement). Only that propellant in contact with the case is excluded from ignition because the thermal conductivity of brass is up to 400 times (280 times higher for chrome-moly