The set includes turned brass barrels.
It is very simple to use in your model, and makes it extremely
realistic. Simply cut off the original plastic barrel and drill a hole
in the remaining plastic parts and insert the metal barrel using
Other versions of Firefly's cannons you'll find in the Master sets:
AM-48-095 - Fairey Firefly - Hispano 20mm cannons with uncovered
AM-48-097 - Fairey Firefly - Hispano 20mm cannons in short fairings