Hi JIm
The 257TED is bassed on the PPC cartridge case.
It is basically a 25PPC with the shoulder pushed forward .075 with a .285 neck
The case capcity is about 2 grains more than the 6PPC.
I use 6.5 Grendal brass to form the cases. FIrst I outside turn the necks to .013 thickenss, then I size the necks and fire them.
The rifle is a Stolle Panda with a Shilen 1/12 LV countour barrel.