So, a friend sent me a photo of his workmate's M&P with a cartridge stuck about where the gas return tube should be. I know nothing about the malf except what you see in the photo. According to the owner, the bolt will not move forward or backward, and, of course, the part of the BCG is in the receiver extension, making normal disassembly difficult.

Questions:

How did that happen?

What do you suggest as remedial action?

Cartridge over bolt.jpg