I've come across a few that were loaded.
One in particular needed to be unloaded, and a twist on the breech plug showed that it was less than tight, so out it came.
From the back end of the barrel the load looked like a bunch of crud. So I pushed a ramrod down from the muzzle and pushed the load out.
And the 'load' was just exactly what it looked like from the rear of the barrel,,, just a bunch of crud that had made its way into the barrel over the years.
No ball, no patch, no powder, just dust, dirt, maybe a hornets nest or two mixed with a bunch of dead spyders.
So loaded ain't always loaded, but still good to be cautious.
John