Anecdote, not evidence, but I switched to a bottle of "Rebel" brand 0.28g BBs (BZ Tactical) last game day, and subsequently experienced... this...
To snap one piston, Mister Borg, may be regarded as misfortune. To snap two looks like shenanigans.
On disassembly, both barrels had 2 BBs roll out, which makes me suspect that one was stuck in the hop.
Of course this could just be an AOE problem, and those are well used cheap JG / CSI plastic pistons being smashed by Big Dragon M140s on 11.1V, and it might very well be entirely unrelated to the BBs, but I'll be binning the Rebels and switching to something else out of an abundance of caution.
Aside, this is why I prefer plastic pistons, because they're the cheapest part to replace, and everything else is intact in both boxes. Sadly, it looks like all aftermarket pistons are steel racked now, so I'll be reluctantly "upgrading".