Mine was the first muzzle loader I had shot so I was a total rookie. I discovered the jag while cleaning it and had no trouble getting it out. I think what was in it was the cork screw like patch puller. Not sure why it stuck at all as it came out easily.

I have a 16ga, William Read & Son, made in Belgium by the proof, and very nice little piece I enjoy shooting, well made and nicely engraved.

I brought home an 1861 Springfield. 58 musket some years back. Did the muzzle dipstick thing, and yep, loaded. I pulled the charge, it was a load of sixes, over a petrified charge of black powder. The powder was absolutely hard as a rock!
May have been loaded over a hundred years, unbeknownst to it's keepers.