Ten sung about weapon (4,3)
I believe the answer is:
sten gun
'weapon' is the definition.
(I've seen this before)
'ten sung about' is the wordplay.
'about' is an anagram indicator.
'ten'+'sung'='tensung'
'tensung' with letters rearranged gives 'STEN GUN'.
(Other definitions for sten gun that I've seen before include "One fires" , "weapon" , "Killer" .)