Round wont load in sks

I just bought an sks and cleaned it up nicely and put about 20 rounds trough it. But then it locked up with a round in the chamber and I couldn't cycle it by hand I had to hit it back with a rubber mallet. Now when I try too load a round in the breach it gets stuck. What would cause this?

Wrong ammo?
Dirty chamber?
Broken case stuck in chamber?
Fouled gas piston?
Too big a rubber hammer bent something?

Hard to say from here!

rc

never mind I brushed the hell out of it and it works now