I think NightHiker nailed it pretty well... I'm a competition shooter with better than average skills, but my carry pistol is a KelTec, and a 50m pistol shot with a .380 is not going to happen on the first shot.

Having run some penetration tests of ChiCom chest ammo rigs for a SOCOM project, they act as a pretty fair bullet proof vest against handgun rounds

hopefully I would have the foresight to work thru the OODA loop (observe,orient,decide,act)to check for alternative cover and escape route

know the difference between cover and concealment...bullets don't go through cover...if concealment is your option, use it and get down

if you have to run standing, wait for a reload with the rifle, or transition to the handgun... most inexperienced right handed pistol shooters will pull shots to the left, so try to move to the shooter's right...

distance is your friend, even with a rifle shot...I would not give up distance for the sake lateral movement, but that is a personal call...lateral motion if a pistol is being used would be more of a priority

if you exit the building... do so with your hands raised, and keep moving...

if you can't get to your vehicle, seek cover behind the engine block of the most distant vehicle you can, then call 911