Hmm. Yeah, one would usually expect to see one hole for the fuse/powder fill. The fact that it goes all the way through and also not hollow except for the channel seems to indicate another use. Many of these types that get confused with mortar shells, coehorn and grenades are often old counter-weights used for mechanisms (gate openers, large clock mechanisms, etc). There is always the small chance that these could still have had some military use, such as in chainshot, barshot, etc lacking some components, but without a maritime provenance, this is just guesswork.
