You will often hear the phrase 'minute of man' (m.o.m.) used in descriptions of SKS accuracy-- the implication being that it wont drive tacks at any distance, but it will reliably put a round in the enemy out to +/-300 yds .
The rear most setting on the sight leaf-- (П, III, 3, D, etc.) -- is the "battle setting." This setting is equivalent to the 300meter setting. In this position, you should be able to hit the enemy from 1-100 meters if you aim at center mass.