The two deepest marks appear to be Provisional proof marks which were put in when they were individual tubes, fired with a high black powder load as a tube with a screw in plug in breech. They were deliberately made deep so that when they transferred from the tube maker to the barrel maker the outside profile could be filed up when joined. After this they would go back as an action and barrel assembly for final proof.
Due to they way hoop stresses and fatigue work a defect on the inside will fail much quicker than a similar sized defect on the outside. Joe has it nailed, perfectly normal and of no consequence.Lets face , theve been fine for @ 125 years, why worry now!
