ss109s won’t stabilize in a pistol length barrel. They impact the target sideways more likely than “pointy end” first. For this reason, I’m not convinced that they they would reliably penetrate a bullet proof vest when fired from a pistol length barrel. Furtheremore, I have never once heard of a LEO being killed with an AR15 pistol firing M855 ball ammo. I don’t believe it has ever happened. this is a virtually non-existent threat. It’s complete BS as we all know, a ruse to deny mil-surp ammo to Americans and nothing more.
Never happened with any pistol. It was all media driven hype, and still is. It is a mythological hypothetical, like all the “blood in the street” stories about concealed carry.
http://gunwatch.blogspot.com/2015/02/556-ammunition-and-switchblade-knives.html