Only guesses what is going on with top edge of that bolt lug? Wear from poor operator technique? Ground away on purpose to allow poor technique? Odds are that chip from the extractor claw occurred from trying to force bolt closed onto a cartridge or a gauge or a "snap cap" that was inserted directly into the chamber - you said there is a thumb cut-out, so a military pattern mauser - MUST be loaded from the magazine - not made to insert one cartridge into the chamber and then close the bolt. A single cartridge must be snapped into the magazine and then the bolt will feed it into the chamber - from below. As GunTech mentions, some can grind that extractor claw to allow it to "snap over" a cartridge rim, but not how it came "from factory", nor how NOS replacements will be made. Compare to a M1917 - it WAS designed for single loading - much larger, different shape "claw" to it.