The most common and most likely answer to this crossword clue is the 6 plus 6 letter word TRACER BULLET
I've seen this crossword clue in Independent
T
R
A
C
E
R
B
U
L
L
E
T
More clues leading to the result TRACER BULLET
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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.