At first I'd say your ammo isn't loaded hot enough to kick the bolt/carrier back. Since the rifle is delayed blowback you are going to need something hot enough to cycle it.
HOWEVER I would wonder if the chamber has any deformations/galling etc. that would grab the case and prevent a smooth extraction. You can look at your brass and youd should be able to see if there's any scratches on it. You don't say if it was difficult extracting by hand, which is a sign the case isn't properly extracting.
Also you may look at the ejector to see if it is rounded or otherwise deformed. If so, you would need to cut it down, weld a piece of 4130 steel to the front, and dremel it down to the proper shape. You could try just welding a big bead of metal but the welding metal is softer than 4130 so you'll find it won't hold up as well over the long term, even after heat treating. You'll most likely have to repaint the receiver since that amount of heat will probably affect the paint.