Re: Marlin .22mag stuck case?
I'm agreeing with MJY. I'd spray some copper cleaning "stuff" in the chamber and just let it work in there for a few hours. (Of course, I'd do the same with the barrel, but it's probably the chamber that's giving you the pressure issue)
Then scrub it out real good with a copper brush soaked in your favorite solvent, followed by a half-a-dozen patches, followed by another copper brush of your favorite solvent, followed by enough patches to soak up the solvent.
That should get you back to "normal".