AA-9 works well for the subsonic loads. I looked it up on the Powder Mfg's websight.
Please let us know how your new Ruger shoots with the Factory Ammo, when you get a chance. My rifle is supposed to be in this week. My only decision is which scope to mount on mine. I'm thinking I'll probably go with the new Nikon 2X7 made for the .300 ACC / Blackout Cartridge. It allows you to be sighted in with both standard & subsonic loads. They only cost about $199 or less on sale.

http://www.nikonsportoptics.com/Nikon-Products/Riflescopes/P-300-BLK-2-7x32-BDC-SuperSub.html

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