Basically, the visibility of the complete object and the shards are keyframed.. The shards are turned into active rigid bodies, a sphere (your bullet) is also an active rigid body, which is keyframed going in the general direction that it will go.

Right before the frame where the sphere hits the plane, the plane’s visibility is turned off, and the shards turned on. The sphere hit the shards, et voila.

With a bullet though, the impact is going to be much more dramatic. You might want to think about adding a field (also keyframed) to blast out the components from the point where the bullet impacts. Just put it up super high powered for like 5 frames or so and that’ll really send them out in all kindsa directions.

You could probably keyframe a gravity field on the shards too, to add some more realistic motion to them (have it assigned to them from the beginning, but just keyframe the gravity field’s magnitude as 0 at the start, then whatever when you want it to kick in).