If you can get a brush down the barrel, I would think a patch wouldn't be a problem. Can you look down the barrel to see if it's obstructed? Is the rod bent, or the jag too big? I can't think of any other possibilities.
Maybe the bolt or the area around the bolt is still loaded up with old grease/dirt/gunk/whatever. Can you get the bolt out?
I quickly searched on the internet but I didn't find a link to a manual or any instructions on how to disassemble the bolt. Got any friends who are gunsmiths?