Here are the pictures of what the inside of the cylinder looked like. At first it was suggested to be leading, but from a new gun with such low rounds through it and also it would not come off with anything I'd say it is part of the cylinder. You can see a tiny bit of leading on the other 5 chambers, bot one of these things is definitely not like the others. I had to put a screwdriver in the chamber from the front and hit it very hard a few times to get the stuck casing out each time. The casing once removed from the bad chamber will not fit into any chamber again, while a casing fired from any other chamber will fit into any of them.
Man, that's brutal machining.