Last gun produced (5)
I believe the answer is:
begat
'produced' is the definition.
(I've seen this before)
'last gun' is the wordplay.
'last' becomes 'be' (I've seen this in other clues).
'gun' becomes 'gat' (US informal term for a gun).
'be'+'gat'='BEGAT'
(Other definitions for begat that I've seen before include "Generated" , "Produced new life" , "Fathered (biblically)" , "Sired" .)