They only come in 1:9 twist barrels. They used to come in 1:10 twist barrels and possibly 1:12 twist years ago. So if it is newer and has a 1:9 twist, you should be good shooting anything from 40-69 grain. 55 grain is perfect for 1:9 twist, so I would stock up on 55 grain ammo for plinking. For hunting, you will want a 62-64 grain soft point for most game.
The Target rifles are .223 chamber only. The Ranch/tactical rifles are 5.56 chamber, which of course can also shoot .223.
My mini 14 will never be sold and will be passed on to my son. It doesn't do anything as good as my AR15's do, but it is such a cool handy little rifle. And 100% reliable through thousands of rounds too.