A gunsmith will add it to his stock (6)
I believe the answer is:
barrel
This could be a double definition.
'a gunsmith will add it to his' is the first definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'stock' is the second definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
Can you help me to learn more?
(Other definitions for barrel that I've seen before include "''Roll out the ..., let's have a ... of fun'' (WWII song)" , "Curved wooden vessel" , "needs some oil" , "VAT?" , "Container for beer etc" .)