Well a few things could be wrong here. This is a gas gun that sat for a long time so check the O-ring in the gas system. You'll need to take the barrel off to get to them. If they are cracked or loose, they will need to be replaced. Look at the gas valve that sits forward of that, is it caked in old oil and carbon fouling?. If everything looks clean, look to the ejector being broken, its a long thin piece that is on the inside of the receiver opposite of the ejection port. There is a small tab that sticks out that intercetps the rim of the shell and kicks it out. Those can be worn flat. Best test is to load a round and hand cycle it. Load one in the chamber, then pull the bolt back hard, the shell should extract out and eject out the side. (do this with the safe on for the love of God
) If it don't then your ejecter is worn or the extractor is loose or broken. If it does then the gas system needs some work.
Another thing comes to mind after the fact. What does the barrel say as far as what shell size its made for. ie. Shooting a 2 3/4 target load will not cycle a gas gun that has a barrel set up for a 2 3/4 magnum or 3 inch. The ports are too small for the proper amount of gas to cycle the gun.