I have researched buying a Mini-14 and Mini-30 to death over the last two or so years.
Accuracy with cheap ammo is a common problem with Mini's. Good quality ammo and not heating up the barrel too much then accuracy is good, not sub-MOA, but usually acceptable.
The 18xxx serial numbers are for rifles made before the last upgrade - thicker barrels, closer tolerances, better accuracy etc.
$500 for a used Mini-14 18xxx series with a scope is not a good deal in my eyes, when I can walk into my local Walmart in Independence, Missouri and get a 58xxx series brand new wood stocked Mini-14 223 Ranch Rifle for $617 + tax. Or can order a Mini-14 in 6.8SPC or Mini-30 for about the same amount of money. The 6.8SPC is a sub-MOA rifle using factory ammo after breaking in the barrel with about 60 rounds. Go to
www.gunblast.com and search for a review of the Mini-14 in 6.8SPC.
There is one aspect of the Mini's that is undisputed, new or old - outstanding reliability that uses an uncomplicated self-cleaning gas system. All I am trying to work out is where in the list of future rifle buys does the Mini fit?