Excessively under guidance, finished carrying a gun (6,2)
I believe the answer is:
tooled up
'carrying a gun' is the definition.
'excessively under guidance finished' is the wordplay.
'excessively' becomes 'too' ('too' can be a synonym of 'excessively').
'under guidance' becomes 'led'.
'finished' becomes 'up' ('up' can be similar in meaning to 'finished').
'too'+'led'+'up'='TOOLED UP'
(Other definitions for tooled up that I've seen before include "Carrying a weapon" , "Armed; dressed with a chisel" , "Carrying arms (slang)" .)