Actually you may be right, but for the wrong reason. This page says that all the rounds would self-destruct after a few seconds, which would leave a telltale puff of smoke - not because they exploded for a shrapnel effect, though that might happen as well, but because the tracer would burn out, destroying the round.
http://en.wikipedia.org/wiki/2_cm_Fl...8/Flakvierling
It also says that some tracerless rounds self-destructed. I don't see how they could make a timed fuse that small, but that's what they say.
As for making something like that in a game, it's probably doable in an original game, but I doubt SH3 could be adapted to do that.