You need to get a "chamber brush," and use that brush and solvent to clean the chamber.
Steel cased ammo gums the chamber with lacquer, carbon blow-by, or both. This will cause cases to stick.
If you shoot steel cased, you will definitely want to bring a cleaning rod when you shoot. If you really stick a case you'll need to push it out with the rod, if pulling the charging handle and tapping the butt on the ground doesn't work.
I use steel cased ammo sometimes, and sometimes it sticks.