Originally Posted by BigNige

Correct . The projectile of a bullet is the end bit (tip) which leaves the barrel

The casing is what held the charge to push the bullet out when it goes bang etc

Thus leaving the casing which was simply the packaging of a bullet

teh best way to describe a mortar albeit crudely is

A locally fired rocket

The mortar casing carrys both the proppleant which launches it into the sky like a rocket the casing here is the rocket body with fins to stabalise in flight

The warhead is also at the tip of the casing which has its own internal firing pin to make it get noisy upon impact with something firm

Nige