Apparently it's made by a gunsmith named Peter Fortner. Supposedly he makes it for everything from double rifles, to drillings of any pattern, to slug guns. I tried looking him up, but I found nothing about this. Just a bunch of Bi-Athlon rifles.
From what little I managed to find, this is apparently available on SxS and drillings of various patterns as well. So I just found it interesting and kind of cool as a concept.A few o/u's out there that have the self regulation feature. Valmet did it with their 412 and 512 series, a few other as well.