I've seen it. Nice build.
The builder may have gone the same route as Ed and others - just file the application with the ATF to approve the cartridge "for sporting purposes". So far, I haven't heard of them ever rejecting an application. Or he could have just copied some other cartridge that was already approved.
If you want to build something chambered in .700 Hubel Express, for example Ed's ATF approval covers you too, since the approval is for the cartridge, not the applicant.