Text says "the barrel marked “Sequoia 265”" so according to Mannlicher Collectors Association`s homepage:

"Early in the Post WWII production Steyr began to list the M-S as “available in 6.5mm”, which was taken in the USA to mean 6.5x54mm. In reality, the weapons were available in 6.5x54mm, 6.5x55mm, and 6.5x57mm. All of the 6.5x55mm and 6.5x57mm appear to be European products, blued bolts, but an US market example may turn up someday."