I posted about this very thing a couple of weeks ago. Mine were opening before impact too. They were hitting 3" higher than the practice heads.I am putting a rubber band around the middle of the blades and no more problems. Tested them with cardboard in front of my target and they are opening on impact now.

I also had post going asking if everyone had shot their broadheads. I guess you missed that one too. You gotta spend more time here.