I recently bought a Civil-War era gun in wall hanger condition from a reputable seller. In the product description, they said "the bore is so full of crud we could only get a rod six inches into the bore." The nipple was broken off so only the threaded shank remained, rusted in.
I got it home and we all know what the first priority was. I kept it pointed in a safe direction and poured warm water into the nipple hole and down the bore... enough to make sure everything was saturated. Whatever was in the bore felt kind of spongy to a probe. I then got after the "crud" with a worm on a stout rod, with frequent, additional doses of warm water. I finally started getting out fingernail-sized bits of debris. These bits, which appeared to be some kind of fabric, gradually got larger as I kept working at it, and I eventually pulled out some pretty good sized chunks. It felt like I hit bottom with the worm, so I poured in some more water and saw it flowing out the nipple hole. Yay!
The gun had not been left loaded. The "crud" was indeed some kind of lacy, knitted fabric, maybe from a fancy curtain. Who knows why it was in there... Some people have weird compulsions to stick things in gun barrels. The rangers at Castillo de San Marcos in St. Augustine told me they find all kinds of odd things in the cannon barrels, put in by tourists.
In any event, we were lucky this time. If it's a muzzleloader that's new to me, I like to check whether it's loaded or not first thing.
Respectfully, if it has powder in it, I consider it loaded. Primed/capped or not, projectile or not. I suppose even a "blank" load could give a nasty surprise.
Best regards,
Notchy Bob