stock mufflers

[feelstranger]

Folks, I'm still running stock mufflers that are in surprisingly good shape - I have no idea if they are PO replacements.
Anyway, just removed them to replace the quickly rusting clamps between pipes and found them to be REALLY HEAVY.  I don't recall thinking they were that heavy the last time I took them off, but that was a while ago.  Is it possible they are full of soot?  No liquid came out when I tuned them upright, though I half expected them to gush water or something.
Are they just that solidly built, or do I have a problem?
I was contemplating plugging one end, and filling them with degreaser of some sort to see what came out.

Nat