Group is told to purchase weapon (6)
I believe the answer is:
pistol
'weapon' is the definition.
(pistol is a kind of weapon)
'group is told to purchase' is the wordplay.
'to purchase' indicates the answer is hidden within the clue (I've seen 'purchasing' mean this).
'PISTOL' can be found hidden inside 'group is told'.
(Other definitions for pistol that I've seen before include "Small firearm" , "A small hand-gun" , "Small gun" , "Shakespearean - weapon" , "Hand weapon" .)