The most common and most likely answer to this crossword clue is the 8 letter word GUNMETAL
I've seen this crossword clue in The Daily Telegraph
G
U
N
M
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T
A
L
Buddy explains!
The straight part
We know that "alloy" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case alloy = gunmetal.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 GUNMETAL mean?
GUNMETAL noun- A type of bronze used for making cannons.
- An alloy of 88% copper, 10% tin and 2% zinc, originally used for making guns.
- A dark grey or bluish-grey colour; gunmetal grey.