Steel cases do not obturate as Brass cases will and because of this, the gas seal between the case and the chamber is not as effective.
A natural result is more carbon and bullet to case sealant will get into the action.
But given the cost advantages, I can live with that if the ammo is surefire and reasonably accurate.
I don't own an SKS at this point, but I do have a ROMAK, a Milled Bulgarian, a B-West Side Folder, a Yugo AKS underfolder and an NM91.
None of these guns like softpointed or hollowpointed ammo.
The only 7.62 x 39 gun in my battery that will reliably run on non-FMJ stuff is my Norinco Hunter. Everything else flattens the bullet tips and/or jams on the projectile tips.