Crossword Genius

Firearm "a small, trivial matter," claims man yet to see the light (7,5)

Ross

I believe the answer is:

assault rifle

I'm a little stuck... Click here to teach me more about this clue!

'firearm' is the definition.
(I know that assault rifle is a type of rifle)

I don't understand the rest of the clue.

Can you help me to learn more?

(Another definition for assault rifle that I've seen is " gun".)

I've seen this clue in The Independent.
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