I'm 80% sure Bioval stopped making them because they were known to be way harder then plastic BB's because they are made with silica, and some fields and big events ban them.I haven't use heavy bios but had some excellent results with Bioval BBBMAX .27g!!
The quality is superb, they are clear but you can see them easy especially if it's a sunny day!
While the opponent can't see them, through the scope looks like they glow!!