Worry about container for rifle (7)
I believe the answer is:
carbine
'rifle' is the definition.
(carbine is a kind of rifle)
'worry about container' is the wordplay.
'worry' becomes 'care' (I've seen this before).
'about' indicates putting letters inside.
'container' becomes 'bin' (bin is a kind of container**).
'care' enclosing 'bin' is 'CARBINE'.
'for' acts as a link.
(Other definitions for carbine that I've seen before include "Light automatic rifle -- nice bra (anag)" , "A short light automatic rifle" .)