I have been shopping for a krag barrel .. And they say dark bore .. I have no idea what this means ... I purchase a lot of guns and restore and resell them so the worse condition there in the happier I am .. Because you can get them cheep cheep and sell them hi hi ... So quite often there so durty you can't even see down the bore ... So I clean them and sometimes there still very dark inside .. So get my shotgun cleaning rod and swabe and but the rod in my drill place polishing compound on the swabe and polish the cartridge camber until it looks like a mirror inside ... And then I get my bore swabe and put polish on it and turn it inside the bore with my drill ... Some times it still dark so I get a new swabe and use diamond polishing compound and so up and down though the bore until it shines like a mirror ... Diamond dust comes in 400 to 50k grit .. And also there is a lot of metal polishing compounds you can get at Walmart ...  I always found it helps to have a nice shinny bore when you sell a gun ... What I have found is a shiny bore don't make you a better shot its just a marketing skeem ... Drak bores shoot just a good ....