I've got kind of an odd situation.
I couple years ago I started making an horn, trying out a couple little little refinements, one of which was smoothing out the transition between the horn cavity and the spout hole. After a couple different attempts, I ended up using a bit of steel wool on the end of a copper wire scrap, threaded through the spout and turned with a drill. Seemed to work ok at the time. I put the horn to the side for quite a while afterwards, and started finishing it last winter. I was almost finished, with the butt end in place and just needed to finish sand the outside and make a staple and spout plug, when I started wondering if it was possible that a tiny scrap of steel wool had gotten imbedded inside when I smoothed out the inside of the horn so long ago....I know looked inside and rinsed the horn to get any loose stuff out when I first did it, and it has been rinsed out a couple time since then, but I'm worried about the possibility of something embedded in the horn that could work itself loose over time and mix with the powder.
When I first thought of this, I put the horn aside and spent Project Time last spring and summer working on a couple other horns as well as a war club with a spike and (most recently) a couple knives. It occurred to me recently that I filed out the spike/blade for the club before I went and went and did some preliminary work on three or four future powderhorns, and that while I certainly cleaned off the bench before I switched projects, it is difficult to get every bit of steel up and theoretically at least it is possible that some stray filings found their way up into those horns when I was working on them. I've only got one vise and a patch of workbench about 18 inches square to work in, so I have to do everything at the same workstation.
I'm good at finding things to worry about, so I might be overthinking this. Still, I'd be curious to hear if anyone else has had to deal with this. I've considered using a soak in vinegar to dissolve anything that might be inside, but I don't know how that will affect the horn or it it will really work well if there is something inside. Heavy-duty magnets are another option, but I don't know if they'd actually pull an embedded bit of steel out of the horn. I could of course just cut these horns up for other things and get some new ones, but some of these are quite nice and I hate to waste them - horns that are roundable and have a nice twist are difficult to find these days.