The most common and most likely answer to this crossword clue is the 8 letter word BANDSMAN
I've seen this crossword clue in The Times
B
A
N
D
S
M
A
N
Buddy explains!

The straight part
We know that "Army musician, possibly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case army musician, possibly = bandsman.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 BANDSMAN mean?
BANDSMAN noun- A player in a musical band, especially a military or brass band.
- A labourer (loader) working with a band of men.