Madbull have made a video demonstrating the quality of their bbs and how to spot low quality ones:
Madbull is know for its dedication in making quality products. One of the most important things you can put in you airsoft gun is the very thing you shoot out: bb’s. Madbull uses high quality plastics from factories that uphold Madbull’s standard of excellence. We demonstrate a very simple way to spot the difference between low quality bb’s and high quality bb’s.
Madbull: better parts, better performance, better products.
(Madbull)