For a variety of reasons, different rounds have different abilities. HE is low pen, wide area. HEAP is lesser area, higher pen (and poorly handled in the extant rules, but easily handled).
With an ACR, I can't drop a BD Troopie unless I use HEAP. But same said HEAP is a waste against unarmored pinkies... for those, slug is more than effective. But that slug will just bounce off a suit of BD-13...
With an ACR, I can't drop a BD Troopie unless I use HEAP. But same said HEAP is a waste against unarmored pinkies... for those, slug is more than effective. But that slug will just bounce off a suit of BD-13...