I am beginning to think that is a generic drawing of the cartridge as I have found that in a number of reloading manuals and some printed by the NRA in their publications. I wonder if anyone other than the author has taken the time to research and measure the cartridges or just accepted this drawing as fact.
I did not know much about the gun or cartridge until I got an action and decided to build a rifle, Matt helped me quite a bit with the measurements and got a reamer made that is well with in tolerances of the original cartridge. That is the reamer I cut my chamber with and it works with the re-shaped .303 brass as well as chambering the original Kynoch ammo.
A friend sent me the article after I was finished with the 1918 Hemburg