This information migh help you!
According to Browning web site, the BLR was made in Belgium from 1969 to 1972 and in Japan from 1973 to present. K was the product code for the BLR. As yours is made in Japan, the 57 certainly means 75. For a reason I ignore, they sometime reverse the two digit representing the year of manufacture. So it would seem that yours would be manufactured in 1975 if that makes sense.
The Constitution is not an instrument for the Government to restrain the people. It is an instrument for the people to restrain the Government!
Today, we need a nation of Minutemen, citizens who are not only prepared to take arms, but citizens who regard the preservation of freedom as the basic purpose of their daily life and who are willing to consciously work and sacrifice for that freedom."
-- John F. Kennedy