Lifetime bronze benefactor
I can't argue with that IvW. I am simply making the point that the whole "proper cartridge" for a double rifle thing may be a bit over stated. Frankly my concern with rimless designs is not extraction but loading. On some rimless doubles, it is possible to slide the unfired rounds past the tab. That could be at least embarrassing in a tight situation. Neither my Sodia nor my S2 (with .375 barrels) will do it, but I had, for a short while, an 8x57 j O/U (rimless) which would do so occasionally.I guess if you are the hunter and using your double for the initial shot you can use what you like.
As a Professional Hunter and guide I would only use a rimmed cartridge in a double, period.
Being willing to pay US$25K on a double for the reason that you own 3 other rifles in the same caliber and it will simplify reloading/ammo issues does not make sense to me.
Go for the proven rimmed version or stay with a bolt action rifle.