There is a gunsmith in Tappen ND by the name of Duane Spooner who has developed a cartridge with Hornady dies that he calls the .257 DGR. It is based on a .260 Rem case necked down to .257 caliber and the neck slightly lengthened. I had him make me one a few years ago on a Rem 7 action. It is virtually the same as the .25 Souper or 25-08. Really like mine and case forming is very easy by just necking down .260 brass and shooting. He calls his business Duane's Gun Repair (DGR). Google him if interested. He has some load data from his load development tests and others posted on his web site. Good luck with your project.
