Remington 870 Jamming Badly!

Post and pics from Remington 870 Forum, maybe you can help?

I have my Uncle’s 870 to work on. He recently acquired it at a low price.
The gun jammed on the first shot.
Badly.
The 12 gauge round was completely stuck in the barrel and the action would not move.
I removed the barrel at home, retrieved the expended cartridge and found a large bulge on the brass!
Upon further exam I found a corresponding “dent” or machining error in the breech of the removed barrel.
I have 2 other 870s to compare this to and neither has this indent.
Attached are links to pics of the barrel and the shell.

Remington 870 Jamming

Remington 870 Jamming

Remington 870 Jamming

Remington 870 Jamming

Remington 870 Jamming

Remington 870 Jamming

Remington 870 Jamming

Remington 870 Jamming