Learner leaving two-barrelled shot gun in the outback? (5-6)

I believe the answer is:

world-beater

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'gun in the outback?' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

'learner leaving two-barrelled shot' is the wordplay.
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'leaving' suggests deleting specific letters.
'shot' indicates an anagram.
'two'+'barrelled'='twobarrelled'
'twobarrelled' with 'l' taken out is 'twobarreled'.
'twobarreled' is an anagram of 'WORLD-BEATER'.

Can you help me to learn more?

(Another definition for world-beater that I've seen is " champion".)

I've seen this clue in The Times.

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