Same blunder happened to me when I first shot my M1900 Mannlicher-Schoenauer. I too assumed it to be a 6.5x54 M-S without a close look at the still dirt-covered Birmingham proofmarks. Results: a perfect hit at 100m and a badly bulged and split case. Only then a closer look revealed the rifle being rechambered to 6.5x55 Swedish and Birmingham reproofed in 1982. The Birmingham date stamp is that circle. B stands for Birmingham, 2 for the proof inspector and H for the year. As F is 1980, H is 1982. Sorry, but your photo does not show such a date stamp. As the caliber designation already is with the SE, your rifle was reproofed quite recently IMHO.

6.5x55 SE is the official CIP designation for modern, higher pressure loads for modern rifles. These loads are deemed unsuitable for the old Norwegian Krag and M94 Swedish rifles. See VihtaVuori Reloading Guide, Edition 12.