Did you recover all the cartridge cases you fired? If so are they all intact? It almost sounds as though you might have a separated cartridge case in the chamber or has been already said some form of obstruction in the chamber.
Take the bolt and bolt carrier out and drop either a dummy round or a live round in the chamber and see how far it goes in- if it goes all the way down to the extractor groove you probably have another problem.
"odio vitae semper dissolubilis"
"Ludo mentis sciem"
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"sic semper purgamentus Yugo kalashnikov! Tempus orbem ad excoquam eorum et dimittetur eis!"