When I did my 455 my first inclination was to machine a close fitting tenon on a custom barrel blank and still use the set screw system for tension. When I measured the bore of the receiver it was bell mouthed by .0015, so I would have to set up the receiver to true it, if i'm going thru all that trouble might as well thread it. While I like the concept of indexing the barrel, I'm not sure I want a cone breech, it just seems delicate and that knife edge might catch or shear a soft lead bullet. But that is just my impression as I have not tried to run a push-feed repeater with a cone breech. Seems to me the real benefit here is in the installation of a custom barrel blank not particularly how it's installed as long as either is done professionally.