A friend of mine has one. It was not made by Steyr, but was built and rechambered by G.Gibbs on a M-Sch 1903 barreled action from the Military production line for Greece, dated on the receiver wall "Steyr 1912" and without the commercial production bolt-hold-down spring. The .256 Gibbs Magnum is named so for it's bore diameter. The .256 Gibbs Magnum case is essentially a 6.5x57 with a shorter neck. My friend uses 6.5x57 brass shortened to 55mm and 6.5x57 load data. The 6.5x55 Swedish case is too fat at the base to fit his chamber.