It says 22 is ok??
They may have changed it. When I checked into it (several years ago), they specifically said no rim fires.
From the Appleseed FAQ:
What caliber is best?In a nutshell: they all are. Appleseed is not caliber-specific. It doesn't matter to us if you use .308, .30-06, .223, .22, 7.62x39, 8mm, .303 — they're all fine. In fact most people opt to use a 22 rimfire such as the Ruger 10/22. Marksmanship and caliber are independent of each other. If you're a good marksman, you'll be able to hit with any caliber. So, if you have an AR-15, SKS, or 10/22 please feel free to join us.