Sorry guys, I had six whole days off at the beach with a friend. I arrived back yesterday night and am buried up to my armpits in alligators again! I think it's a gas problem and not chamber but could be wrong. I was under the impression that these replacement barrels are chrome lined like the originals but looking at the polishing job, it appears that's not the case. I've seen a similar problem before and it wasn't the piston or an oversize gas port but a worn out gas cylinder. I still have some used but excellent cylinders here to try if that's the case. Contact me directly if you want to send it. Send the complete rifle so I can go through it and range test it too for you to be sure it's properly repaired.
Brian