I recently ground the clip slot off and drilled and tapped a Spanish 98 Mauser marked corona, 1952. This was by far the hardest receiver I ever worked on. The back bridge was as hard or harder than the receiver ring. It dulled bits and broke taps and wore the teeth down in the taps. I ran a propane torch in the holes to anneal it, but didn't help much. Has anybody else worked on one of these and was it this hard?