The most common and most likely answer to this crossword clue is the 6 plus 8 letter word ROCKET LAUNCHER
I've seen this crossword clue in The Times
R
O
C
K
E
T
L
A
U
N
C
H
E
R
More clues leading to the result ROCKET LAUNCHER
Buddy explains!
The straight part
We know that "weapon" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case weapon = rocket launcher.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.