This tells you a bit about the origins and intended purpose: 6.5 Grendel - alexanderarms.com.
I'd say 250-300m for deer. A 7.62x39 is generally considered to be a 150m-200m deer gun. The Grendel moves a much higher BC bullet at a touch higher speed, extending the effective range. For smaller game such as wallabies & goats, I'd say it's good for as far as you feel you're able to get good shot placement.
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