I like it.
I think you need to consider some more design issues, and some game balance
issues.
First, the PPC cartridge is going to be smaller than a conventional ETC round
from the same barrel. This is because you will need a "container" to
direct the force of the plasma bolt that is bigger or thicker than a
corresponding HEAP cartridge casing. I still think it would be a nasty weapon
but this will help bring it down a notch.
Which leads handily to my next issue. Cardinal rule: anything the NPCs get
the PC will get eventually. Give *them* a compact weapon capable of defeating
battle dress (and light vehicle armor???) and your in trouble. Make sure that
there are some limiting factors; I would make the range very short ("due to
the extreme weight of the round"), the cost per round very high, and/or the
recoil very high. A fully automatic version would be right out.
Ok so much for the voice of reason. Now think about this; why have the bolt
go off on impact? seems to me you could do some serious area damage with the
addition of a simple proximity fuse, or a timer fuse which causes the round to
go off at a set distance from the barrel. It would act a bit like a plasma
shotgun; the round leaves the barrel at 400 m/s, at 20m it goes off-creating an
effect like there was a plasma-gunner standing there. I would go for a more
diffuse bolt which attacked a cone, use the rules for flechettes but with
the "fragments" being hot plasma. I wouldn't dare to guess a damage after
sermonizing above.
Pete