I have a RigidBody2D setup, and it supposed to break into smaller pieces when it detects a collision from any other body in the group "bullets". The thing is, it's only detecting some of those collisions. Here's a video of it in action:
It's pretty unreliable in its detection when you shoot at it from far away, but it becomes pretty reliable when you're at point blank range. Other than that, it seems entirely arbitrary whether or not it will detect collision.