An absolutely perfect post, and one that I agree with, as long as the person who buys such a double follows your lead!

The problem is, in most cases, the buyer who buys a double rifle chambered for a rimless or belted rimless cartridge is usually one or both of two things. He is "NEW" to double rifles, and/ Or is buying on the cheap, or both. In my opinion, most of the guys who buy a double chambered for the "BELTED RIMLESS" cartridge are guys who have "MAGNUMITIS", and think that they can hop up the cartridge as they always have in their bolt rifles. In so doing they either get very poor results, or even damage the rifle in the process. Of course this is not always the case as you are an example of the other side of that coin. These are the guys who tend to use bullets like the very hard mono-metal X-bullets in these doubles because that is what they used in their bolt rifles. Then they want to get every FPE of energy they can, and then when they bend something in the rifle with these hot loads the rifle becomes unreliable even when cleaned religiously.

The question you asked about the reason for the ignoring of the 375Flanged is because of the mindset of the average double rifle buyer who tends to go bigger because he only considers the double rifle for an in close defense weapon. There are many who post in all the double rifle forums and have owned, and used double rifles for years who simply can't make themselves understand that a double rifle can be used for longer range shooting as well. Searcy has a raffle going right now for a Classic double rifle to raise funds for his grand daughter’s baseball team! If I happen to win that rifle it will be chambered for the 375 Fl Mag in a nine pound double rifle and fitted with scope rings and mounts. I will simply buy 100 new 375FL cases, and load my own cartridges for it. Because the double rifles chambered for the 375FL mag are so hard to find, I too have been tempted to buy a double chambered for the 375H&H mag, a cartridge that I truly love in a bolt rifle. However I tend to use my rifles for hunting of dangerous game, and so far have resisted buying a double rifle for that purpose in anything but a flanged cartridge.

I think a guy who knows a few things about double rifles can surly get away with using a double rifle chambered for a belted rimless cartridge, but IMO, most who do so are not people who know much about the double rifle, and therefore I will not recommend a double rifle with a rimless cartridge that may be used to face dangerous game to anyone! They are fine for hunting deer elk and moose, or black bear over bait from a tree stand but even in the smaller chamberings there are plenty of flanged cartridges for them as well. If everything is perfect in a double with rimless, and belted rimless cartridges it will work fine in double rifles, but you and I both know that Mr. Murphy rarely lets everything be perfect when it is sorely needed!