I'm about to draw gun in temper (8)
I believe the answer is:
mitigate
'temper' is the definition.
(I've seen this before)
'i'm about to draw gun in' is the wordplay.
'about' is a reversal indicator.
'to draw' becomes 'tie' (synonyms).
'gun' becomes 'gat' (US informal term for a gun).
'in' indicates putting letters inside.
'im' backwards is 'mi'.
'tie' going around 'gat' is 'tigate'.
'mi'+'tigate'='MITIGATE'
(Other definitions for mitigate that I've seen before include "Make less intense or serious, say offence" , "Lessen the gravity of" , "Soften" , "Extenuate" , "Make less harsh" .)