Sounds like an ejector problem: worn out or broken off?…. when you install the barrel does the ejector fit into the slot, or is the barrel free to rotate a little? Unfortunately, this it one of those repairs that requires
specialized tools to properly rivet the spring to the ejector. Perhaps Scattergun Bob, our 870 guru, knows a shortcut fix, or can help with finding someone in your area to do the work; otherwise, you may be shipping your receiver to someone like Simmons.