Thanks to all for your comments. As I see a lot of interest I´ll tell the story.
I always wanted a double rifle. I was inspirated by the pics of the ivory hunters of the old time and their stories. Last but not least this threads with your comments influenced as well.
But the criteria I had would have made it a costly thing, if I buy a Krieghoff, Merkel or other... I always liked exposed hammers more than hammerless and I wanted the rifle to be used in Europe and Africa on plains game and Big Game, as well. My first choice was a Pedersoli Kodiak. I had one checked by a gunsmith and the proofhouse and both where not convinced on the strenght of the system. I looked around and found a spanish manufacturer who makes a rifle in different chambers, that includes 9,3 and 444 Marlin. He also makes this types of shortguns. I gave him a call and he would make a rifle in 9,3 and 12 Gauge. He does not do a bigger cartridge. So I checked the CIP data, chamber pressure and made some calculations on backthrust. Out came that the 500/465 has a bit less pressure as the 470 and backthrust is just about the same as the 444 Marlin has. I spoke with serveral gunsmith asking about my plan. They all said, to not see a problem. The worry I had is, I had to take the responsability of the proof-firing. If the rifle holds up, OK if not....I loose a lot of money.
On the other side, the 465 cartridge is only ~10% more expensive then the 470 and there is Romey nearby for loaded cartridges and Horneber and others as well, for brass. As this cartridge has the same mother as the 470, there was not much to think about.
Well, the comments took away my worries and my gunsmith provided a set of 500/465 barrels to the manufacturer. We discussed the finnish, engraving, barrel contour, wood... I told him that I want optional optical sights on the 9,3 set, which he does not do neither, so we agreed that he prepares the barrels in the white and proofed (except the 465) and fit them to the system. My gunsmith had to do the honorable task to install the sights, cut the chambers and proof the 465 and regulate the barrels.
Well, all this started 2 years ago and now it´s time to use it. It never was my intention to have a wallhanger...

thanks to all Tom