It's going to make a poor shotgun with the rifling still in it. With the rifling so worn, it probably isn't much of a rifle either. After the Civil War, a lot of surplus rifle-muskets were reamed out to 20 gauge and turned into shotguns and there is no reason why you couldn't do this now. You could bob the barrel and cut the stock down too. That would save some weight. Sporterizing military surplus long arms isn't a new thing.