100 year old guns do not have mirror smooth bores and tend to collect more minor crud like things in their bore surface. It does not matter. Clean it, dry it and use a good oil to cover the surface to protect the bores. That's all that is required. Working to remove 100% of everything is a lot of extra work. Look at it this way the gun lasted 100 years with that crud in/on the bores it should last another with it in there.