In special relativity, simultaneity depends on your reference frame. In one reference frame, event A can occur before event B, but in another, event A can occur after event B. There is no absolute ordering of events that are separated in space time, unless the events are causally connected.

>But if the bullets looked at each other they would only see themselves moving apart at the speed of light.

Additionally, the reference frame of the bullet (photon) is not defined. There is no reference frame where a photon is at rest, so you cannot use special relativity to consider the perspective of the "bullet."

If the bullets were traveling at almost c, each bullet would regard the other bullet as traveling at almost c. You may observe the bullets moving away from each other at almost 2c from your reference frame and hitting the walls simultaneously, but the bullets would not. See closing speeds and other examples of apparent superluminal speeds.