Army extremely eager to secure large place for gun (7)
I believe the answer is:
holster
'place for gun' is the definition.
'army extremely eager to secure large' is the wordplay.
'army' becomes 'host' (host is a kind of army).
'extremely' says to hollow out the word (remove centre letters).
'to secure' is an insertion indicator.
'large' becomes 'l'.
'eager' with its middle removed is 'er'.
'host'+'er'='hoster'
'hoster' placed around 'l' is 'HOLSTER'.
(Other definitions for holster that I've seen before include "Revolver' cover" , "case for weapons" , "Where piece goes" , "It can carry 17 Ac" , "Gun sheath" .)