Ive had a mini-14 for years, great reliable rifle, but no comparison to the accuracy of an AR at distances of 100 meters of more.
I have a glock 22 and would never trade it on a mini-14 (2 completely different purposes).
Dont get me wrong, the mini is as accurate as most rifles in its class, but not great at all. I found that ammunition does not effect the accuracy much at all with my AR, my Ruger target rifle, my 10/22, or my mini-14. The differences are so minute from the cheapest target ammo at 100 meters to the best, and even reloads (my own), that I would measure it in 1/16-1/4 inch at 100 meters.
Anyone having accuracy problems that are very big at 100 meters are not with ammunition, Id say its the "nut behind the trigger". Human error is 99% of accuracy problems unless you have a real malfunction with a weapon of a round.