Simunition is the trade name of them. They're incredibly common in that kind of training/simulation situation, because they let you use your standard weapon with only slight modifications (internal, no BFA or anything like that) and approximately ballistically match the standard round, and are close enough for sound and recoil.
They're pretty intense and can hurt a lot, my dad's been in several training situations with them, and when he got hit in the upper thigh, couldn't walk right for a few days. Most of the intensity comes from the basic fact that you're using your standard weapon.