Perhaps certain to lack volunteers if more precise (5)
I believe the answer is:
nicer
'more precise' is the definition.
('nice' can be similar in meaning to 'precise')
'perhaps certain to lack volunteers' is the wordplay.
'perhaps' is an anagram indicator.
'to lack' indicates named letters should be taken away.
'volunteers' becomes 'ta' (abbreviation for Territorial Army).
'certain' with 'ta' taken away is 'cerin'.
'cerin' is an anagram of 'NICER'.
'if' is the link.
(Other definitions for nicer that I've seen before include "better" , "Even more 7 down!" , "comparatively agreeable" , "relatively pleasant" , "more lovely" .)