Originally Posted by Daniel_

B and M are both bilabial sounds in English, and in many forms of transliteration between languages get reversed.

I don't know for certain, but is there a now obsolete method of tranliteration that renders the B where you would render the M now?

For example, in Chinese transliterations, I grew up being taught about "Peking", the capital used by "Mao Tse Tung", and now I teach my daughter about "Beijing" the former capital of "Mao Xedong". Did Korean do something similar?