Still in need of a new filling (13)

I believe the answer is:

muzzleloading

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

'still in need of a new filling' is the definition.
The definition suggests an adjective which matches the answer.

'still in need of a new filling' is the wordplay.
'still' becomes 'muzzle' (muzzling is a kind of stilling).
'in need of' says to put letters next to each other.
'a new filling' becomes 'loading' (loading is a kind of filling. I am not sure about the 'new' bit.).
'muzzle'+'loading'='MUZZLELOADING'

Can you help me to learn more?

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.