It was not designed too. It only allows the round to keep the inital damage when passing through. It gives a placebo affect where you think it does more when really it is not. Basically they way it works as if you shoot something and that thing would take of .25 damage from teh round. Meaning a round doing .90 damage would suddenly only do .65 with out impact. With impact that same round passes through the object and does around .75-.80 or close to it. So more damage passed through so less rounds required to kill. The same with people but people probably reduce the damage by less then say a wall. So up close a .90 round would possibly still do about .80-.85 damage meaning you kill a little faster. And when several players are near by those rounds that pass throuh do more damage to the second player meaning less rounds to kill them is needed.

It is not adding damage, just keeping more of the initial damage with each object it passes through.