It's a fixed sort of charge (7)
I believe the answer is:
bayonet
'sort of charge' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'it's a fixed' is the wordplay.
I cannot really understand how this works, but
'a' could be 'one' and 'one' is located in the answer.
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found in the answer.
The remaining letters 'bay' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for bayonet that I've seen before include "Neat boy (anag.)" , "Blade fixed to a rifle" , "one's attached to one's rifle - that's sort of fitting" , "Type of light bulb fitting" , "Knife fixed to the end of a rifle" .)