We were told by the County cops last year that even a screwdriver will penetrate a vest.
anything that will seperate the weave will go thru the standard issue LE vests. kinfes, arrow and small pointy rounds like 17 HMR, and the 17 rem go right thru.
Just keep shooting until they stop.
now if they have ceramic turama plates and the like, you are going to need a full power rifle to get thru them.