Nearing new situation where a gun is effective (2,5)
I believe the answer is:
in range
'situation where a gun is effective' is the definition.
'nearing new' is the wordplay.
'new' indicates anagramming the letters.
'nearing' anagrammed gives 'IN RANGE'.
(Other definitions for in range that I've seen before include "Able to be seen" , "becoming available as target" , "within striking distance" , "Within gunshot" , "An easier target" .)