Generally speaking, when Ive tested different calibers you need 2000-2100 fps+ to get through the tougher IIIA preparations. Speed and cross section matter.
I found that regular old soft IIIA gives up earlier so I wanted a tougher standard IIIA.
These are just 6x6 composite side plates. I dont like the YouTube videos where they shoot up a bunch of vests multiple times. If you see how the fibers interact, you can get remote weakening after more than one shot so I always test my important things on a clean, fresh plate.