BC only scored one position in the "top-selling-manga-in-japan-by-volume" ranking, and that position is the last one, number 100. Even The Promised Neverland surpassed it with it's second volume and position number 93.
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And it's position in the "top-selling-manga-in-japan-by-series" ranking is nothing special either.
Shokugeki no Soma also placed in the top 30 without an anime in the first half of 2014, position 20, and 1,394,312 volumes sold.
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Boku no Hero Academia placed 10th in the first half of 2016 with 2,135,591 volumes sold.
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Granted that this ranking went from November 23, 2015 to May 22, 2016 and that it's anime aired eight episodes from April 3, 2016 to May 22, 2016, but i'll take a wild guess and say that even without these 8 episodes from the anime it would have made it into the top 30.
If anything these rankings only show a huge decline in physical volumes sold from last year to this year. The places 19 to 30 from this year wouldn't have made it into the top 30 last year, Haikyu and Terra Formars went down 1 million sold volumes each from last year, Nanatsu no Taizai went down almost 1 million sold volumes (probably due to Nakaba's health problems and hiatus), Gintama lost almost 50%, Prison School didn't even make it into the top 30 this year which means it sold less than 50% compared to last year.