Habit of the Queen, perhaps, to take a turn loading twelve-bores (4)
I believe the answer is:
robe
'habit' is the definition.
(I've seen this before)
'of the queen perhaps to take a turn loading twelve-bores' is the wordplay.
I cannot really understand how this works, but
'of' could be 'o' and 'o' is present in the answer.
'queen' could be 'r' (r is abbreviation regina. e.g. in ER ) and 'r' is present in the answer.
'take' could be 'be' (being is a kind of taking) and 'be' is present in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for robe that I've seen before include "Formal vestment" , "Gown or dress of office" , "official dress" , "Gown, rich dress" , "Christening garment" .)