IIRC - The U.S. Krag receiver went through 120 machine operations. To speed up the process, receivers were held in fixtures in pairs, so that machining operations were performed on two receivers simultaneously.

That odd 'angled' cut on the OP"s receiver looks like it could have been a mistake caused by something getting out of whack during a shaping operation???

IMHO - If something was cosmetically or dimensionally wrong with a part, during the course of Krag production, it would have been noticed with all the inspections and gauging that went on. Likely, the part would have been 'tossed into a scrap bin'. A receiver was likely "Right" before giving it a serial number and facing the prospect of paying royalties.

Some experimental Krags, like Cole and Metford rifling tests and Parkhurst Device trials, were documented by serial number.

Serial numbers are a handy thing to have on prototype, test, and trial rifles for identification and comparison purposes.

(I'm not a Machinist, but, my father sure was! I'd like to see more details on that Krag. It's an interesting puzzle).