Research I did some years ago show it to be quite rare. The main reason is probably due to the very modest velocity increase with the AI chamber. The .308 is already pretty straight so the typical AI blowout does not increase the capacity much at all compared to the expansion ratio. Look at the .30-06 with its much larger capacity yet not that much more velocity. Heavy bullets in the .308AI cut into the capacity a lot, reducing any gains even more. Ackley didn't even list it in his books.
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