Uh, try a slingshot instead.
Seriously, it depends on the twist rate of the rifle. You need to know when it was manufactured and what the twist rate is so we can give you a relatively decent answer.
You should be able to get away with some of the Black Hills blue box 68 grain loads in your rifle. They won't buck the wind like one of the heavier bullets available, but, it is fairly easy to get them at shows and the like. They are pretty accurate out of an AR with 1 in 9 and 1 in 7 twists, so you should be ok with them in your mini.
If I remember correctly, the mini could have either a 1 in 7 or 1 in 9 twist.
TFLers, correct me or verify me on the twist rate that ruger has used if you could.
Good shooting,
Slick