Great tactic rep deployed in exercise to improve accuracy (6,8)
I believe the answer is:
target practice
'exercise to improve accuracy' is the definition.
(exercise to improve accuracy with a weapon)
'great tactic rep deployed' is the wordplay.
'deployed' indicates an anagram.
'great'+'tactic'+'rep'='greattacticrep'
'greattacticrep' anagrammed gives 'TARGET PRACTICE'.
'in' acts as a link.
(Other definitions for target practice that I've seen before include "Working on aim" , "aiming to improve with this?" , "Learner's shooting session" .)