[Mike Cecil]

I didn't think it was that much of a mystery, Dave.

The 18pdr 'Shrap' - can't remember the exact term off hand (Edit: 'Shell, Shrapnel, QF, 18-pdr') - consisted of an outer casing, with a wide mouth, threaded to accept a fuze holder for the VT-P (Variable Time - Percussion) fuze. The thread of the holder was shallow and short, which is significant. Held within the casing were a whole bunch of steel balls (Edit: actually either mixed metal of antimony-lead or cast iron, not 'steel'), held in a medium (I think, shellac?: Edit: it was Resin) with a hollow down the centre of the shell to the base. In the base was a small bursting charge, from memory, Black Powder. Can't remember if the hollow tube was a long fuze or open. (Edit: the tube was a central metal tube that screwed into a steel disc that sat above the bursting charge, which was contained in a tin cup in the base of the shell casing.)

The shell functioned by the time fuze, at the pre-set time of flight, flashing down the centre of the shell to the bursting charge in the base, or by impact on target. The bursting charge then did two things: slowed the outer casing, and pushed the contents (all the balls) forward, popping the fuze holder and spent fuze from the shell casing and pushing all the balls through the wide mouth of the casing. The balls were directed forwards along the axis of the shell at the time of initiation (termed the 'cone of dispersion'), like a shotgun round, rather than scattered in all directions as would happen if the shell casing was designed to disintegrate (which would also take a far larger bursting charge). The now vacant and slowed casing, usually still intact, fell to earth. The fuze also fell to earth more or less intact. The medium (resin) holding the balls in place inside the casing disintegrated as the balls were forced forwards through the wide mouth, and served to increase the 'puff' signature of the burst to aid in observation, along with the black powder bursting charge.

The HE shell casing, by contrast, was designed to shatter when the explosive charge within was initiated, the destructive force being both the explosive (concussive) force and the jagged metal fragments from the casing.

Mike C