Thanks for the replies so far, I really appreciate the help!
I am just field stripping the rifle to get to the extractor spring, but I ran into another problem:
I unscrewed the locking bolts to pull them out, they are very loose but cannot be pulled out. What's wrong now?
As far as I can judge about the chamber, it seems to be ok. The rounds can be chambered easily by hand and the cases dont show any sign of scratching, dents or things alaike.