In fort, help to pronounce on part of rifle (8)
I believe the answer is:
stockade
'in fort help' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'pronounce on part of rifle' is the wordplay.
'pronounce' becomes 'ade' (I am not sure about this - if you are sure you should believe this answer much more).
'on' is a charade indicator (letters next to each other).
'part of rifle' becomes 'stock' (part of a gun).
'ade' after 'stock' is 'STOCKADE'.
'to' is the link.
(Other definitions for stockade that I've seen before include "Protective fence of upright stakes" , "Wooden enclosure" , "Fortification" , "Defensive or confining enclosure" , "defensive structure" .)