Yes it is. Many years ago I developed a load and loaded up a couple of packets of 8x51 rounds for a guy who had a Mauser K and reloading dies for the cartridge. I just ran 308 Win cases into the FL die and loaded them up using Norma 196gr .318" bullets the owner supplied. Can't recall the powder I used, probably 4064, but used heavy bullet 308Win data to get started and worked up an accurate load.