So, I got out my Rice barrel clamp and Rice breechplug wrench and a 3 foot piece of pipe and proceeded to remove the breech plug. It was perfectly indexed and a perfect fit to the breech face and not much more than finger tight.
All the others I have pulled took two two men and a boy to get them out.
Anyway what ever the "thing" was it fell out and disappeared when I pulled the plug. There is some flash metal in the bore from where the liner hole was drilled but that can be easily ground off with a small diamond bit.
I think what you see across the bore is dirt, one cleaning patch and it was gone.