870 Wingmaster fails to eject reliably

[Helengrace]

It sounds like you've already done a lot of work on the shotgun, and it's good to hear that it cycles cleanly with live ammo. Based on your description, it seems like the issue might indeed be related to the ejector spring, or possibly the ejector assembly itself. If the Sully replacement system isn't an option due to the lack of holes in your receiver, one possible solution could be to check with a gunsmith to see if they can retrofit a similar system or modify the receiver to fit a more compatible ejector assembly.

Another thing to consider is to try a more powerful ejector spring, as sometimes aftermarket parts can be a bit stronger than factory ones and might help improve ejection reliability. It might also be worth investigating if the magazine tube or shell latches are causing any interference with the shells, as that could be contributing to the jamming issue.

I hope this helps, and I wish you the best in resolving the issue.