To try and address your question: I haven't used Biovals myself so here are the tests I use to determine BB quality (hardly exhaustive, but good enough for most purposes):
1. The surface is glossy, without mould lines, pits or uneven texture.
2. Using some pliers to crush a BB, it should deform but stay in one piece, rather than shattering into lots of potentially gearbox destroying pieces.
3. Using calipers, check if the dimensions and variance match the stated values on the package. If the package has tolerances of greater than +/- 0.01mm, or if the package doesn't mention the tolerances at all (a big warning sign), don't use them.
4. Cut a BB down the middle, there should be no significant gaps or air bubbles.
To better explain xav1982's concern, FPS on its own does not indicicate how much a BB will hurt, rather it's impact energy, which is determined by a both a BB's mass and speed. A 1kg brick will hurt a lot more travelling 20FPS than a 0.2g BB at 330, so when you fire a heavier pellet from the same gun it'll hurt just as much even if it's travelling slower. When a field places FPS restrictions, it's actually a hidden energy limit rather than a speed limit, because they usually specifiy 0.2g BBs to test with. To reduce the energy of your shot, replace your gun's spring with a softer one, m100s are standard and will bring your FPS with 0.2s down to about 330.
Airsoft is where expensive things go to die.
Last edited by Bellerophon; August 15th, 2013 at 12:23..