It's the firing that makes weapons heated (7)
I believe the answer is:
gunshot
'it's the firing that' is the definition.
I can't judge whether this definition defines the answer.
'weapons heated' is the wordplay.
'weapons' becomes 'guns' (gun is a kind of weapon).
'heated' becomes 'hot' (synonyms).
'guns'+'hot'='GUNSHOT'
'makes' acts as a link.
Can you help me to learn more?
(Other definitions for gunshot that I've seen before include "One fired" , "Range of a specific weapon" , "Source of report" , "Firearm's range -- no thugs (anag)" , "Fire" .)