The most common and most likely answer to this crossword clue is the 5 plus 4 letter word RAPID FIRE
I've seen this crossword clue in Independent
R
A
P
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E
Buddy explains!

The straight part
We know that "Barrage of questions" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case barrage of questions = rapid fire.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does RAPID FIRE mean?
RAPID FIRE adjective- (of a gun) Able to fire bullets in quick succession.
- (of a series of questions, etc.) Delivered in a rapid continuous stream.