Metal barrel gents rolled (8)
I believe the answer is:
tungsten
'metal' is the definition.
(I know that tungsten is a type of metal)
'barrel gents rolled' is the wordplay.
'barrel' becomes 'tun' (tun is a kind of barrel).
'rolled' indicates anagramming the letters.
'gents' is an anagram of 'gsten'.
'tun'+'gsten'='TUNGSTEN'
(Other definitions for tungsten that I've seen before include "Steel-grey metal" , "Light-filament element" , "Element used in steels" , "Hard metal used in steels" , "Snug tent (anag)" .)