Tested, bound to be about right (5)
I believe the answer is:
tried
'tested' is the definition.
('try' can be a synonym of 'test')
'bound to be about right' is the wordplay.
'bound' becomes 'tied' (I've seen this before**).
'to be about' is an insertion indicator.
'right' becomes 'r' (common abbreviation).
'tied' enclosing 'r' is 'TRIED'.
(Other definitions for tried that I've seen before include "Tested" , "Had a crack" , "Made an attempt" , "Proven by experience" , "Essayed" .)