You got there, Mikael!
The only other 'BK' I have seen had "Fabrique en Suede" or something like that on the other side of the tang - french for 'made in Sweden' so that particular one was an export for the french market. In 1876 they were using Bessemer steel, but that is probably just coincidental too as yours doesn't look that old. It isn't the initials of any of the founders (1804 = Olof Heljestrand, 1825 = Johan Olof Heljestrand, sons were Carl Viktor and Nils Fredrik. Interesting question!
Regards,
Neil