For the AR-15, 300 BLK would be a good option. Ballistically, it's not that far off from being a 30-30. Alternatively, there's the 6.8mm SPC or the 6.5 Grendel.
The 25-45 Sharps is also something to consider. an 87gr bullet at 3000 FPS is nothing to sneeze at.
I think the sharps is interesting. Kind of like clambering an AR-15 in 25-06.
I only question barrel life, but I suspect ammo cost will prevent most from doing mag dumps at the range.
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