Type of card enclosing precious weapon (7)
I believe the answer is:
sidearm
'weapon' is the definition.
(type of gun)
'type of card enclosing precious' is the wordplay.
'type of card' becomes 'SIM' (as in a SIM card).
'enclosing' means one lot of letters goes inside another.
'precious' becomes 'dear' (I've seen this before).
'sim' enclosing 'dear' is 'SIDEARM'.
(Other definitions for sidearm that I've seen before include "Officer may carry this" , "One may be fired" , "weapon" , "Piece" .)