will reduce volume of a typical propellant column by about 15% and that such a level of compression will effectively eliminate porosity – data gathered by this author, circa 1996, and first presented in edition seventeen of Handloader's Digest.
This loss of porosity prevents gases that might penetrate into the mass from doing so. Moreover, gas penetration that occurs before such loss of porosity occurs and any that occurs as a result of any residual porosity through the mass, cannot be significant because no place exists where such gas can go, after reaching front end of charge mass – by deliberate design, front of cartridge presents an almost perfectly sealed container. Hence, as nascent granule combustion generates gas pressure within zone near base of charge, that zone expands and thus drives the remaining charge forward and; in response, the forward portion is simply compressed.
Within this compressed zone, to a certain depth, granule combustion gases can penetrate with sufficient heat to result in granule ignition; beyond that depth, it is impossible for sufficient gas to pass into or through this portion of the charge to introduce sufficient heat to ignite the granules. This discussion represents a reciprocal argument – that portion of the propellant mass that primer does not directly ignite is the compressed portion described above. The point here is to understand that in most reasonably large cases with normal loads, such an initially unignited volume always exists. Ballisticians within the military munitions industry have proven this in