Yeah search methylone theres hundreds of threads about dosages and experiences all over the web as well as on blue light. Oh wait just realized you said bk-MBDB not bk-MDMA which is methylone.
butylone / bk-mbdb is an even milder entactogen than methylone with even milder effects. Common dose is about 300mg, iirc, with doses as high as 500mg being taken with no negatives really noted (http://www.erowid.org/experiences/exp.php?ID=82188). Check out the erowid vault on b1 / butylone here: