Damn, here in case you don't want to deal with Federal's interstitial
I doubt that the zipper would have significant effect. The teeth are anchored in fabric and would be easily broken apart and passed through. Even if the zipper would cause some early expansion of the round and/or slowing down, it would still send a significant shockwave through the body. Also, in a gunfight you would not be firing a single round. The next round would come a split second later and be offset at least a fraction of an inch and missing the zipper.I have been an HST guy for about 15 years now. I typically run 147 grain 9mm in my full size guns and I go for the HST Micro 150 grain in my pocket 9s.
That said, I wonder what happens to rounds that hit a zipper. Does it even effect the round at all ? If you are aiming center mass there has to be a greater than zero chance that a round will hit a zipper on a jacket on a hoodie ( or even God forbid a pair of jeans !). Some youtube ammo reviewer that is running low on video ideas should tackle the zipper variable with hollow point ammo.