Syk joined the community
I know this is old but doing the math a 5.56 UTM has the equivalent KE of a .20 doing 560 fps... approx 2.9 J. it is a .45g projectile doing about 375 fps. From personal experience they hurt... bad. they also have a little steel marker bb inside the assembly that likes to embed itself in unprotected flesh. I caught a couple of these in the face, the scars make cool stories.