Not exactly the same thing, but Vudoo Gun Works supplied barreled actions with a semi-coned breech a few years ago, leaving plenty thick enough surface around the chamber so that there was no issue with ignition, enough so that it still required shallow extractor slots. Their reason for this style breech was to provide an area for suppressor crud to fall into when a shooter set his suppressed rifle (with the suppressor still attached) butt down into a rifle rack during a match. With a conventional flat breech with slots, the crud that often fell out of a suppressor when the rifle was racked would tie-up the bolt because of the tight bolt/breech dimensions. The semi-cone provided an area for the crud to fall into.
I set 22RF bbls up in a super spacer/indexing fixture on the mill table to cut extractor slots. When cutting slots for a custom action where the maker supplied me with a drawing giving breech dimensions (Stiller 2500XR, Vudoo), having a good DRO like the Newall simplifies things a good deal, but it's still a bit nerve-wracking to cut the slots to leave only .005" between the edge of the chamber & the slot. For factory actions like CZ457 and Win M52, I've just copied as close as possible the slot dimensions of the factory bbls. It still makes me wish for a CNC mill and the programming skills to set up RF barrels...lol
Kevin's cuts look to me to be an excellent compromise between a flat & coned breech - leaving plenty of flat breech surface for reliable/consistent ignition, yet with a good deal more leeway for slight variation in the indexing of the bbl in the action for extraction.