Im sorry to hear youre another person with an inaccurate mini
cant say that its a rare occurrence. I hope your friend has the time/patience to deal with it, or the awareness to move onto another rifle. The thing about the mini, is its generally not an out of the box accurate rifle. If your looking for something your going to go pdog hunting with strait out, then it isnt a good choice. If your willing to put time and energy into it, its a very good project gun, much more rewarding then just bolting on parts.
My own mini (newer 581) shoots well, and there are a few things that can be done to improve the accuracy of any mini. Bedding the action helps, as well as shortening the barrel and/or adding a strut. A trigger job is actually pretty easy to to on the mini, but takes care and patience to do right. Cryo treatment has its proponents but ive had a hard time believing in it myself (well see as the only gun ive seen it done on was garbage going in, garbage coming out). A muzzel weight (brake, flash hider, or boss system etc.) has been known to cause a serious improvement of the mini for some odd reason, again ive never heard a definitive answer as to why. Other bits that make living with a mini more enjoyable are either an adjustable gas block, or a set of ASI gas tubs, Im running a .040 on my mini and its now tossing brass in a 45* arc at 10ft or so. A buffer will help as well, keeps your scopes from dying an untimely death, and your action from getting beat too badly. Handloading has given me little real advantage in my own mini (unless i load out very long to touch riffling, then this gun will shoot right with my bolts), but in a friends rifle 70grn speer ssp over 4895 gave very very good results, this is a load im going to try next in my rifle.
If your interested in what ive done to mine i can tell you, and give you accuracy figures, but minis it seems are more individualistic then most rifles, so i dont think the info would really be of any benefit.
If your interested take a look at the perfectunion forums, pretty much everything to that ive found out (actual information, rather then people just upset because they got something they didnt want) about minis has come from there.
On a note, i just reread the original post and figgured out HOW inaccurate the rifle is being. It does sound like a odd problem, and i WOULD contact Ruger.