It’s looks like you’re on to it! I came across that particular rifle as well, but did not make that correlation. That’s very interesting and makes sense. It would be interesting to compare other 10.75x68 chambers as his had very little throat if I recall correctly. However, if one is proofed for a 3,2g charge I suppose that rules out an original 10.75x68 chamber anyway. Thanks for the clearer picture of the DWM book, what a resource!