mosins can be VERY accurate rifles. since most people shoot mil surp through their nagants, acccuracy isnt exactly a hot topic. but if your rifling is in good shape, and you are using decent commercial loads, the nagant can achieve awesome accuracy. if you throw a scope on there its even better; although it is absolutely not necessary
my own nagant, which is a '44 isvesk M44, can shoot VERY respectable groups at 100yd even with mil surp hungarian craploads. i can easily get a 4-6" group @ 100yd on a sandbag
even the worlds deadliest sniper of all time, who in ww2 was credited with over 542 confirmed kills with his rifle, used none other than an M28 Mosin nagant rifle....
and he preferred iron sights over the scope
(by the way his name is Simo Hayha)