Frank, glad to hear your not hurt and sorry about the truck. Would your Peabody take the 375 NE 2.5" Flanged?. Think of it as a hornady 405 winchester case cut to 2.5" and necked down to .375 caliber with either a 1x18" twist or 1x16" twist. Suprised that Double D hasn't suggested this already as I know he has a martini set up in this caliber. Have come to the revelation that it would be way cheaper to have you make up a rifle for me than use one of the hi wall actions, fit and chamber a barrel and do the wood and blueing. Every time I see the link to your site I stop and go over there and spend about 15 minutes drooling. You do make some fine rifles. I'd like to stick a good redfield international globe sight up fromt and a redfield international for the rear sight and see what she would do. Take care and hope your aches and pains go away quickly. Frank

The 375 2 3/4 is not appropriate for a side hammer Peabody.

Unless Frank wishes to standardize on the .45-70 case head, the .375 2 1/2 NE which Singleshotlover mentioned strikes me as a reasonable choice. It dates -- if I recall -- to the late 1890s, and the CIP pressure standard for it is well below that for the .33 WCF. Perhaps DoubleD objects to the cartridge length? The .33 WCF is 2.8" with a 2.1" case vs. about 3.1 and 2.5 for the .375 NE.

Frank, ok according to "custom cartridges" by Ken Howell the 375 2.5 uses origional 375 2.5" cases or 9.3x74 rimmed cases. However the 38-72 uses 375 cal bullets and to make cases we can take the new hornady 405 winchester brass cut them down to 2.5" and voila, we have a cartridge that uses 375 cal bullets either jacket or cast, readily available brass, and with a 1x16 or 1x14" twist should be able to handle up to and including 300 grain jacketed or cast bullets. And it would be an American design course its a little bit late by about a hundred years. But still in keeping the spirit by calling it the 38/405 cartridge. At a guess the whole length of a loaded round with a 300 grain bullet would be about 3" possibly more. Guess that this is mere wishful thinking on my part. But its nice to dream once in awhile. Frank

KWK, sometimes I get so carried away I tend to confuse other folks. And even myself. What I was looking for is sort of an American version of the 375 2.5 cartridge. Since the 405 brass as made by hornady is reasonably cheap and available that is what I based my version of the 375 2.5 cartridge.
Would be able to use a lee enfield #1MKIII action or even the #4 series actions. But having seen the peabody rifles on their website had thought that it would have been a natural. As you said the pressures are low. Since I'll only shoot a few jacketed rounds through it to see how it shoots, I'll then start using cast bullets. Should be easy to get to shoot accurately. The reason also for the 2.5" length was to allow it to function through a lee enfield magazine. The early lee speed sporters were chambered in the british version of the 375 2.5. Always drooled over them, but being retired, and on a very fixed income there is no way I'll ever get the money in one place and at one time to get one. Classic styling and beautiful rifles. So at least now you can understand my thinking. Course I could always use a P14 action (which I have) and do the same thing. But wouldn't quite be the same. Always liked the single shots, especially the martini's and of course the peabody's. Got a couple smaller ones like the cadet and BSA 12-15. Still have plans on doing a 12-15 into a small 30 caliber cartridge gun. Maybe as I get older (62) I'm trying to go back to the simpler things as far as rifles are concerned. Used to cast my own bullets for a variety of cartridges but have been stagnant for way too long.
Frank

Assuming the cartridge length isn't a problem, I still find the .375 2-1/2 a reasonable chambering. Certainly, it's no more unusual than the .33 WCF, other than -- perhaps -- that older actions to my eye look better with a "fat" cartridge, such as on the .45-70 case head. I think it splendid they offer the rifle in .33 WCF. 

Reflecting on it, I suppose were it my rifle and I wanted a .375, I'd go with the .38-56 improved. The case capacity will be close to the .375 2-1/2 and with the operating pressures of the .33 WCF, it would be a very heavy hitter, all with relatively cheap brass.

KWK, couldn't agree more with you on the 375 2.5 cartridge. When funds become available pgt will make a reamer for me that will basically be a 303 british case necked up to 375 caliber with a straight neck one caliber in length. This should work in the lee enfield receiver that I've been working on.
And should be able to seat out 375 cast bullets with the gas check even with the bottom of the straight section of the neck. 
Double D, Thanks for the offer of your reamer to Frank. I too am curious as to wether or not it would make the turn. But please tell me why you do not think this cartridge is wrong for this rifle. Not trying to start any flame wars. 
Frank, thanks for not blowing me off regarding the possible chambering of your beautiful peabody rifle in either the 375 2.5 inch (british version) or mine based on the 405 winchester cartridge. your comments were most welcome. and do understand that a new company in today's economic climate has to do what it must in order to survive and get ahead.
Ive enjoyed all the discussions from all of you. And no one got flamed either. But learned from folks that have way more experience than I do.
Maybe I should take the barrel off the ruger 1 1/2 rifle I have and have someone put on a 375 caliber barrel with 1x14 twist and get it rechambered in my version of the 375 2.5 and a long throat for shooting long 375 cast bullets. Haven't shot it but once and could get douglas barrels tofinish turn a barrel in the varmint taper that they use for their sendero's or varmint synthetics. With the breech of the barrel opened up so as to be able to be installed on the ruger action. Don't think that a 1x12 twist as I first posted will allow higher velocities due to the faster twist. Heck I may be old but the brain is still firing on all 6 cylinders. Frank