thank you everyone for your advice and comments.
I’m leaning to thinking it’s an assembly screw up. Also notice the receiver is an alloy. This is a Rizzini. The ejectors are a harder steel.
Any reason I can’t sand and polish these out?
It appears in the photo that the burr protrudes past the face of the receiver. If that is the case, I'd take a very fine file and remove it from the face. I would leave the mark on the top of the receiver alone.
I kinda figured that was a Rizzini. I have a Connecticut Shotgun M21 O/U that uses a Rizzini style action. Mine also has a slight mark on the top of the receiver. When I bought it, a young man working for the FFL that received it for the transfer came out from his back room with it out of the box and assembled. He apparently wasn't used to assembling a shotgun like this with trunnions and spring loaded ejectors. When I got it home I noticed the mark.
It's easy to do, sorta like the "idiot scratch" on a 1911 from the slide stop. You have to be a lot more careful assembling a shotgun like this then a Browning with a hinge pin and ejectors that lie flat to the the monoblock. I have to say, I'm not crazy about the design. I much prefer the Browning approach to ejectors. The advice in assembly, go slow and be careful that the trunnions are properly engaged before trying to close the action.