Crowhunter,
You kinda right, but not really.
The plastic tip doesn't "initiate" expansion as much as the BIG hollow-point under it. This is required so the "stem" of the plastic tip can be seated. Slow-motion video shows the plastic tips don't "drive down" into the bullet, but float out in front of it as the bullet expands, then drift off to the side.
Bergers don't actually have a hollow-point, because the tip is pretty much completely closed. You can't even push a typical sewing needle into it. Instead, the front end collapses backward, because the lead doesn't extend anywhere near the tip, rather than expanding outward. Which is why Bergers penetrate 2-3" before expanding, instead of opening up as soon as they hit hide.
