Place for a gun mostly in part of Germany (8)
I believe the answer is:
holstein
'part of germany' is the definition.
(German state)
'place for a gun mostly in' is the wordplay.
'place for a gun' becomes 'holster' (a gun goes in a holster).
'mostly' means to remove the last letter.
'holster' with its final letter removed is 'holste'.
'holste'+'in'='HOLSTEIN'
(Other definitions for holstein that I've seen before include "German region" , "Breed of black and white dairy cattle from northern Holland" , "Source of beef" , "dairy cow" .)