Show bombshell with casing removed (4)
I believe the answer is:
expo
'show' is the definition.
(short for exposition, a large exhibition)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for expo that I've seen before include "Large international exhibition" , "World fair, e.g. Seville 1992" , "Show" , "Large international fair" , "Major international fair" .)