If you're even mildly involved in real-life shooting, either as a hobby or professionally, you're going to spot a lot of gaffes.
I can understand simple continuity errors. By the time a film has been cut, edited, recut, edited again, Foleyed, CGI'd, etc. it's got to be difficult to keep track of whether the protagonist's gun should be empty. It doesn't take anything away to assume the hero simply reloaded offscreen.
But these things are a totally different matter:
-The mythical "Glock 7"
-The slow-motion sequence showing an entire round of ammunition going downrange, not just the projectile,
-Ammo "cooking off" somehow acting the same as if it were confined in a barrel (I'm looking at you, "Paycheck!"),
And I can't count the number of movies/TV shows where
-Someone "cocks the hammer" on a gun that doesn't HAVE a hammer, like a Glock.