The first reference to the Krag shell necked down to .25-Caliber is by F. W. Mann circa 1904.
These early rifles used what I call the same method of loading as the Schuetzen rifles of the day. A breech-seated bullet in front of the case. A base-band was used to seal the bore and keep the primer from moving the bullet up the barrel.
This is a chamber cast of one of Dr. Mann's barrel (1909) having the outside case diameter the same as the bullet diameter. You just dropped a bullet into the chamber and seated a loaded case.
The name of all of the Krag to .25 caliber cartridges were called the ".25 High-Power" back in the Mann-Niedner days.
