The main issue of accuracy with the mini 14 is the twist rates have been a moving target over the production years. I have an older one with what is supposed to be a 10 twist, but actually measures out to be around 10.5 inches per turn... and a newer one with the 9 twist.
For a few years in the late 70's/early 80's, they were using a 7 twist, and this is where they really got the rotten reputation for being minute of barn door... especially when shooting the 55 grain surplus fodder.
You need to find out what twist the gun you're getting is (if it's a newer model, it'll be a 9 twist), and use decent ammo of the right bullet weight if you want accuracy. I realize that AR's will shoot light bullets from 7 twist barrels pretty well, but the Ruger barrels won't do it--or so it appears...
My older gun will stay about 1.5 MOA if you don't get it hot. Then it trails off low and left. The newer gun doesn't seem to be as accurate... but I have not tested it with heavier than 55 grain bullets yet.
On the plus side, they'll tend to be more reliable than an AR. It has often been said that if Uncle Sam had sent Mini-14's to the troops in Vietnam, there would have been a lot fewer of our guys coming back in boxes...
And the newer M-16's have given similar trouble in the desert, it turns out. We even had our guys in Iraq using confiscated AK's for some time, or worse yet shooting their M-16's with panty hose stretched over the actions to keep the sand from clogging them up.
Dan