Pistol defenses look easy to do but many details… Yes, when something happens it can take a split second and it is all over. In Pure Krav Maga you learn what is the fastest time that something can happen (efficient attack), and then you learn to deal with it you need to have efficient approach and application for defense. So to make that split second reaction most efficient you need to break down the attack and defense into its small components and get rid of inefficient habits of execution.
The components of defense include efficient use of your time which is most likely a split second and your body of which you thrive to minimize the response time by responding on time using the correct sequential execution of your motions to promote maximum efficiency. Gun Defenses should never be a series of impressive theatrical response...
The training methods designed in a way that will facilitate the execution of the correct sequential execution, will promote response with approach that will have the best tactical solution as well.
Very important details of training put weight on the details of a motion or series of motions called techniques, and the most realistic application of techniques and response to scenarios using prioritization of the response of your brains and body.
Getting out of the line of fire: Well if it is faster to kill the attacker then move away from the barrel with your whole body you leave it to the sniper. Before you get out from the line of fire you might want to consider if it is faster to move the line of fire away from you.
Cars are much slower than bullets, and you have the time to see them and move away if you did see them and did not panic.
It is easier to move the head away from a barrel than move the whole body away. Still the timing is also depending on who is reacting to who and how long the reaction time takes. So you need to chose the quickest option although they might all work in certain conditions, since it has the greater probability to work.