ok read through an nobody has stated the obvious and to my american friends this should be basic import gun 101 .
the SKS has an internal 10 round mag with a hinged floor plate. there are sks with detachable mags OR have had "duckbill" mag conversions like that from tapco.
the version capable of taking AK type magazines is called *drumroll please* the SKK. this is the true detach factory designation.
versions have been made specifically with side rail mounts which accepted early PU type optics.
Shooting wise they go from tack drivers to can't hit the side of a barn with most being somewhat in between. my own 20" barrel norinco version was rather rough on the outside metal work included and took weeks to get all the cosmoline grease out but during service rifle matches,and even while under pressure shooting for points in original form was capable of 25mm groupings with 125gr wolf FMJ ammo. however after 300m it's really a guessing game, yes it can hit further ( its round is lethal even after 1.5km +) but achieving realistic accuracy past 1-500m tops is the questionable especially without optics.