Great day at the range, and had some spare kevlar to experiment with. It stopped FMJ 9mm, but it would hurt something fierce. Then we tried 5.56mm, just to see... I don't know if it even slowed down. If it did, it probably just expand a little more. Which wouldn't be good. Just in case you didn't read the instructions (or are curious about Kevlar), our plates are the only protection against high-velocity rounds.