If you check my content, hprentice, yonks ago i tested a pair of those cheapo £3 mesh jobs to destruction - they did surprisingly well. IIRC It took 14 shots point blank striking in pretty much exactly the same place to get them to fail enough for a BB to pass through, but it was definitely over 10. On full auto it took more shots - 17 I think. That was at 370-ish FPS.
I'd trust them to take anything that could be fired at me in one go during a skirmish (and I did until I found a pair of Hero Sharks going cheap in a closing down sale), but I wouldn't go back into the field wearing any that had been dented.
What it comes down to is that they do not fail catastrophically, because the plate the holes are punched out of just isn't tempered enough for spring or hardness - my guess is that it's mild steel cold rolled to put the perforations in, which squashing would also improve the strength a bit. The mesh deforms under impact and it will stretch a lot further than, I at least, would have imagined before it tears and even then it doesn't let a BB through until the tear has been sufficiently widened by successive hits in the same spot.
If you work out rates of fire vs reaction time and the chances of BB's hitting the exact same spot without losing much of their energy by hitting each other, you realise that the only way that an accident could happen in which BB's could make it through cheap mesh is if the wearer was pinned down so they couldn't move their head and the shooter either did it deliberately or somehow fell in such a way that they jammed their finger on the trigger in a manner that they could neither remove it nor move the gun away...
---basically, my hole can it happen! Which is no doubt why, so far, it never has happened.
