I think this is stuff we should probably already know. I mean, I'm not a gun guy myself but pretty much knew these plot devices and explosions that action movies overuse were bull shit. I have fired a few rifles when I was younger, but I don't own a gun and I never have. Well, other than a BB gun when I was a kid that we used to take camping and shoot holes into pop cans.
The biggest one that annoys me is the cocking of the gun that you see constantly in movies where the character is trying to get someone to talk. They don't give them the information they need, even with a gun in their face, so they cock the gun and then the person starts spilling their guts about whatever they want to know... That always drives me crazy! As if the gun wasn't going to go off when the trigger was squeezed? OH NOW YOU COCKED THE GUN AND I MIGHT DIE. The threat was just as real as it was before.