JD_Zincavage-
Ned Roberts wrote many articles about his .25 caliber cartridges in The American Rifleman in the late 1920s and early 1930s. Unfortunately, the magazine was rarely indexed then, and digging out the material is tedious.
However, I found the following information in Sharpe's
Complete Guide to Handloading, 3rd edition, 2nd printing, copyright 1953, on pages 358 and 359. It seems to be pertinent to your questions, including loading.
.25 G&H and Niedner-Roberts
The .25 Griffin & Howe and Niedner-Roberts cartridge is the one originally known as the .25 Roberts. Throughout this book, however, it is being designated under the above full name, as it is entirely different from the .257 Roberts cartridge sold commercially. The .25 Roberts cartridge was never manufactured by any firm and was the original Roberts development designed by Ned H. Roberts of Berlin, N.H. Major Roberts began experimenting with the .25 caliber back around 1909, cooperating with Dr. Mann and A. O. Niedner. Since that time he has been playing with it continuously and has had coutless different barrels and bullets and cases made to his specification. The original .25 Roberts was the 7mm cartridge necked down to .25 caliber but having a long sloping neck. Also, at least two times, the length of the neck was altered slightly, so that the Niedner Roberts and the Griffin & Howe Roberts were somewhat different.
...
It should be thoroughly understood that loading data for the .25 Roberts and .257 Roberts must not be interechanged. ... Most of the loads given for the .257 Roberts can be used in the .25 Roberts , but one can by no means reverse the procedure. Maxiumum loads in the .25 would cause extremely dangerous pressures in the .257 due to the sharper angle or slope of the bottle neck.
...
The .257 Roberts was originally designed by the Reemingtons who were experimenting with the .25 Roberts cartridge in an effort to produce it commercially. The long slender taper of the shoulder, however, did not appeal to them because of its manufacturing complications. Accordingly, they changed the angle entirely so that the .257 cartridge cannot be shot in rifles chambered for the .25 caliber Roberts. It was first produced as the ".25 Roberts", but Captain E. C. Crossman insisted that to release it that way would be to invite severe complications. He suggeste the change in name to .257 Roberts, which Remington immediately accepted.
I have no idea whether Sharpe is correct in his statement regarding the relationship between loads for the .25 Roberts and the .257 Roberts. Once you have some cases fireformed for your rifle, you can check relative case volumes.
Use your rifle wisely.
--Bob
