6.5-06 or AI is still the 6.5-284 ballistics/case capacity....really no difference.
If you want a 6.5mm stick with the 6.5-284 but in at least a 22" barrel.
If you want a 6.5mm in an 18" bbl, then do what GWH recommends and use a 6.5 Creedmoor...just seat the 147gr ELD-M out right out (get the reamer in 6.5 Creed with a long throat).
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