It is some sort of defect (looks like etching) but if you can't feel it with a patch (so it's not any sort of significant obstruction) I'd just see how it shoots.
One of my rifle bores has a minefield of pits (nice shiny pits) that are visible with the naked eye at the muzzle end, but still shoots okay.
Last edited by mauserand9mm; 06/02/20.
