Took a pistol, cornering wild mammals (6)
I believe the answer is:
okapis
'wild mammals' is the definition.
(type of mammal)
'took a pistol cornering' is the wordplay.
'cornering' indicates a hidden word (the answer is trapped or cornered by the clue).
'OKAPIS' is hidden within 'took a pistol'.
(Other definitions for okapis that I've seen before include "Giraffe-like creatures" , "Relatives of the giraffe" , "They're similar to the giraffes but smaller" , "Giraffe-like animals with shorter necks" , "African mammals" .)