Executive Director, Technical and Special Effects for Oh Penny Pictures, LLC.
Here's the key to all this - you have to LOOK like you're shooting a real gun. I have an entire arsenal of airsoft that I have used in films that look ultra real with wear marks that appear on actual firearms. However, all that realism means nothing if your shooter doesn't follow through with a little body acting.
It doesn't take long to get an actor in the groove of what that gun would be doing if it were real when the trigger is pulled. However, it totally pays off in the editing process. Guns recoil straight back and THEN the barrel rises (generally speaking). So, if you have an actor who has to fire a handgun for a scene, you train them to emulate that motion. It brings about a realistic shooting sequence where you then can add the CGI all day long. If done right, it will be hard to tell the difference for the average viewer. (Firearm enthusiasts will always know because... reasons.)
So, yeah - paint it to look realistic, but don't forget the actor is the other half of the battle, so to speak.