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If you are a reloader then the .300 Blackout gets interesting, brass cases, boxer primers, and bullet selection. Of course Ruger is against reloads in their semi-auto rifles. Their have been some KA_B00Ms with reloads in the Mini series.
While .300 is a great cartridge for a reloader (you can reload it from range scrap, .223 cases with crushed necks, etc), the days when it was primarily a reloader's cartridge are long past. Factory ammo abounds, and I think it is only a matter of time before outfits like PRVI and Wolf start loading it. There is already Fiocchi FMJ Blackout ammo available.
One additional advantage that I forgot to mention in my reply to Greg above, is that the .300 is optimized for performance in shorter barrels. I'm planning a 10" barrel for my SBR, and that's honestly a bit on the long side of typical from what I have seen (8"-9" seems to be most common). 7.62x39 takes a bigger performance hit going to a barrel that short, and as mentioned, the better BC of the .308 bullets means that the Blackout actually retains more energy at longer ranges anyway.
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