What about a little nano technology?

Some composite carbon-tungsten alloy risers that weigh less than 1 lb with a material structure that counteracts vibration at the molecular level? Granted if they built one today, it would cost about 1.5 billion each But that sort of technology is coming.

Nano machines are also being developed that can react to light. Eventually you could have a camo coating that mimics your surroundings like a chameleon just like in "Predator."

And how about a string and cables made of something like spectra fishing line? 1/5th the diameter and mass with all of the strength? That would have to be good for a few fps? ( I know, spectra cuts easily, I'm just using that as an example!)

What about an inertia driven expandable head, maybe with a mercury core that deploys the blades sort of like an airbag?