The website-with-an-obvious-viewpoint, BearingArms.com is reporting that polymer bullets are under development. The bullets are actually a polymer/copper composite (no idea of what the relative amounts of each are), but since they have less mass than a traditional round, there is less recoil when fired. But more interesting than the materials is the shape of the bullet. Take a look:
This opens the door to future designs that are even more "creative", since working with plastics is generally much easier than working with metals. And since we already have 3-D printed guns, it won't be too long before we have 3-D printed bullets too.