sharpness is how "sharp" it is. In CC less sharpness = less terrain rape. So if it has negative sharpness but a high velocity it just beats clones to death and leaves the terrain virtually unharmed. High sharpness = terrain rape regardless of the velocity. Think of it as scissors and paper. The sharper the scissors the easier the paper is to cut. the duller they are the harder it is to cut.

Yeah, sort of like this scale:

0 - Totally blunt, will NOT pierce, regardless of impulse.
1-20 - Poor piercing, needs lots of impulse to pierce anything.
21-50 - Mediocre piercing, still needs a good impulse.
51-100 - Decent piercing, which doesn't require too big an impulse.
101-200 - Good piercing, suitable for heavy bullets.
201-500 - Great piercing, either for snipers, or for light bullets.
501-1000 - Careful now, this thing is pointy!
1001-2000 - Getting more like acid...
2001-5000 - Seriously sharp, will probably just drop through anything.
5001-10000 - Lazor. Nuff said.
10000+ - ZOMG RAEP

Kind of random, but it does give people a slight idea of how the
sharpness value acts like...
If the sharpness is 0, only mass and velocity causes the damage.