Explosive piece about too much working (9)

I believe the answer is:

guncotton

I'm a little stuck... Click here to teach me more about this clue!

'explosive' is the definition.
(I've seen this before)

'piece about too much working' is the wordplay.
'piece' becomes 'gun' (I've seen this before).
'about too much working' becomes 'cotton' (I can't explain this - if you can you should believe this answer much more).
'gun'+'cotton'='GUNCOTTON'

Can you help me to learn more?

(Another definition for guncotton that I've seen is " Type of explosive".)

I've seen this clue in The Telegraph.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.