What is this?

[cre34]

[ptmn]

Looks like a piece of a broken off ejector

[ptmn]

Guess I was wrong, I did a search on Google and it looks like 410 Ejectors have two pieces. Take a look at this eBay auction photos for a 410 Ejector before it closes. It shows an Ejector and that piece you have.

https://www.ebay.com/itm/Mossberg-500-Ejector-Complete-Set-410-GA-Original-/333647220027

[cre34]

Thanks, I couldn’t find anything on Google.

Curious why the .410 has the extra piece and the 12 and 20’s don’t. ��

[ar15barrels]

Probably to space the ejector closer to the chamber centerline since the 410 is so much smaller than a 20ga.
410 is probably built on a 20ga receiver.

[kendog4570]

It's a kicker to move the ejector into alignment with the cartridge rim.

[cre34]

Thanks for the answers everyone!