It's probably an optical illusion. I have heard of that before. Seems like I see it myself from time to time but like you I don't believe you would get decent groups if it was doing that. You would have erratic groups. I shoot an agressive helical fletch and notice it in certain light. Other's say the same thing about it flying like a bullet though. So, I ignore it. I get very tight groups so I believe it's an illusion.