Half of police carrying first gun (6)
I believe the answer is:
pistol
'gun' is the definition.
(pistol is a kind of gun)
'half of police carrying first' is the wordplay.
'half of' indicates taking half.
'carrying' indicates putting letters inside.
'first' becomes 'ist' (**).
'police' halved is 'pol'.
'pol' going around 'ist' is 'PISTOL'.
(Other definitions for pistol that I've seen before include "Shakespearean character" , "Hand-held firearm" , "Hand weapon" , "Spoilt these guns" , "Small firearm" .)