Editing Shell (projectile) (section)

==Background==
Gunpowder is a [[low explosive]], meaning it will not create a concussive, [[brisance|brisant]] explosion unless it is contained, as in a modern-day [[pipe bomb]] or [[pressure cooker bomb]]. Early [[grenades]] were hollow cast-iron balls filled with gunpowder, and "shells" were similar devices designed to be shot from artillery in place of solid cannonballs ("shot"). [[Metonymy|Metonymically]], the term "shell", from the casing, came to mean the entire [[munition]].

In a gunpowder-based shell, the casing was intrinsic to generating the  explosion, and thus had to be strong and thick. Its fragments could do considerable damage, but each shell broke into only a few large pieces. Further developments led to shells which would fragment into smaller pieces. The advent of [[high explosives]] such as [[TNT]] removed the need for a pressure-holding casing, so the casing of later shells only needed to contain the munition, and, if desired, to produce shrapnel. The term "shell," however, was sufficiently established that it remained as the term for such munitions.

Hollow shells filled with gunpowder needed a fuse that was either impact triggered ([[Artillery fuze#Percussion fuzes|percussion]]) or time delayed. 
Percussion fuses with a spherical projectile presented a challenge because there was no way of ensuring that the impact mechanism contacted the target. Therefore, ball shells needed a time fuse that was ignited before or during firing and burned until the shell reached its target.