I had a single dud out of about 100 rounds through my SKS the first time I went to shoot it with 1970s Czech surplus ammo. What I get every now and then is where the ejected brass gets caught by the bolt as it moves forward before the brass is completely clear of the action. Not a big deal, just be careful not to double charge as I almost did it once with a live round that was in the chamber somewhat and pulling the bolt back (to free the previously stuck brass) began to chamber another round. I saw what was happening and I was glad I simply didn't let go of the bolt like I normally do. I simply dropped the magazine, let the excess rounds fall out, and the partially chambered round fell out as well. After locking the magazine again, I loaded each round by hand and continued to shoot.
Be prepared to clean your SKS after using surplus ammo. The chrome bore is quite good at resisting corrosion that would have certainly spelled the end of the bores on my Mausers. After 100 rds of surplus, the bore still looks like new (I wasn't able to clean her for another 2-3 hours after my range trip as well). I found that my firing pin became somewhat sticky so I took the bolt completely apart and wiped down every part and now the firing pin doesn't stick anymore. This will probably be one of the biggest issues that you will run into if you have an SKS with a free floating firing pin. No real biggie to take apart either, I use a rubber mallet, a cutting board with a depress in it, and the punch tool from the cleaning kit. You would be amazed that many of the parts on the SKS (even the cleaning rod) can be used for a multitude of functions to assist in cleaning the SKS. She truly is a weapon for the field.
I went through about 40 rounds of Czech surplus in relatively quick semi automatic fire (about 1.5-2 seconds per shot) and the barrel and action was getting hot so I gave it a break for 20 minutes and switched to my Mausers. When I came back, she was cooled down and ready for more surplus.
After opening the crate of surplus ammo (once you remove the sheet metal cover as well), you will come across little blue cardboard packets. Each packet contains two stripper clips with 10 rounds each (20 rounds per packet). I simply loaded them into the action, let the bolt go, dropped the safety, and let the target have it.
Great little carbine for the price, same goes for the ammo. She is a keeper and I am glad I put my doubts aside months ago and picked her up along with a crate of ammo.
I found her to be much more accurate with the bayonet mounted.
If you are looking to disassemble your SKS and get all that cosmoline out (and later on surplus ammo gunk build up), I highly suggest this guide as this is what I used to help me take mine apart. It is quite comprehensive and easy to follow. The SKS virtually requires no tools to take it apart and she is quite easy to maintain (the number one reason I admire the SKS and other Russian/Soviet firearms).
http://www.surplusrifle.com/sks/carbine/index.asp
This has been my experience with my SKS and surplus ammo, I hope this helps you out.