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Maybe you should search for some .375 H&H Flanged 2 1/2 inch NE cases. I had a significant amount of them 5-10 years ago and I suspect you can find some now.

https://www.handloadermagazine.com/cartridge-board-4

bushveld,
The .375 H&H Flanged has a head diameter of .454-.456" and the cases I need have.427-.433" head diameters. The 38-55 has about .422" head diameter, which is close enough to be safe and not require swaging the head, even though a little short. I have swaged heads before, but this is a lot more trouble than adjusting the rims (only a lathe job) and putting up with slightly short cases. I have resigned myself to possibly swaging case heads when my last bag of original cases runs out but had decided to use either 30-40 Krag or .303 British. I have 30-40 cases on hand, but also have a rifle, so I would likely buy currently available .303 cases. I do have a little .375 H&H Flanged 2 1/2" ammo but will save it in case I find a rifle. In my condition I would rather have one of those rifles than the Flanged Magnums.
Mike

DerAmi;

I agree with you about the desirability of the cartridge that started all the popularity of .375 caliber cartridges well over 100 years ago ---the .375 H&H 2 1/2" Flanged NE. Graeme Wright has a lot of good things to say about it as well, and significantly how easy it is to regulate a double rifle with it. Loaded with modern propellants and obtaining about 2,000 fps velocity at the muzzle and nearly 2,400 ft lbs of energy with a 270 gr projectile it is a cartridge of more than 100 years of age that can be used in many difficult situations.

When I built the .38-55 Mcpherson cartridge based double rifle, I wanted to try to duplicate the ballistics of the .375 H&H 2 1/2" Flanged NE in an old classic American made shorter cased .38-55. And although I was successful in doing that with a 255 grain projectile, I have to load the .38-55 McPherson up to around 32,000 psi with 38 grs of IMR 3031 (the pressure is according to the virtual reality ballistics software I use) . This pressure is the near limit of what this shorter case will do and when loaded at greater pressure for proofing the .38-55 McPherson case is a "throw away". I purchased a chamber reamer and cartridge cases for the .375 H&H 2 1/2 inch Flanged NE at the outset of my thinking of what cartridge I was going to use in the DR, and now after shooting 300 plus rounds through the DR, if I were to do it over I would have chosen the .375 2 1/2 inch cases. I would have had more flexibility with propellants for similar chamber pressures with that size cartridge case---one has to be very careful with heat sensitive 3031propellant especially in 90-100 degree ambient temperature summers in the South. I did experiment with other propellants with the .38-55 McPherson and the .255 gr projectile, but the speed and accuracy was best with 3031. And in that regard for the safety of such pressures I contoured the barrels to have 1 inch diameter at the breech and for 2 1/2 inches forward from the breech.

Kindest Regards;
Stephen Howell

Stephen,
I am jealous of your ability and your work.
Mike