I made up a .260 for my daughter, which had a Jeff Lawrence Barrel on it. Jeff had chambered the barrel the barrel a bit over 1/10" to long. So- I initially had it threaded as received, with the long .260 Rem. chamber. Thus, I simply necked 7x57 down to .260 for a crush fit and fire formed them.

The case had the front end of a .2560Rem, with 20 degree shoulder, but the length of the 7x57, thus, was sort of an improved .6.5 Mauser due to the .454" shoulder diameter, but with the Rem. sloping shoulder.

Case capacity was 60gr., same as the .6.4x284. With Re#19, it's 26" bl. drove 120gr. XLC's at 3,308fps.