Shot zero with gun (8)
I believe the answer is:
howitzer
'gun' is the definition.
(howitzer is a kind of gun)
'shot zero with' is the wordplay.
'shot' indicates anagramming the letters.
'zero'+'with'='zerowith'
'zerowith' is an anagram of 'HOWITZER'.
(Other definitions for howitzer that I've seen before include "Gun firing shells at a steep angle" , "Shell-firing cannon" , "Short, heavy gun fired at an angle" , "Short-barrel cannon" , "Military weapon" .)