I always find it hilarious finding such goofs.
My favorite so far is in The Walking Dead. Now this is my favorite series on TV right now next to Southland...in the very first episode, Rick tells a deputy to make sure he "had a round in the chamber, and the safety off". Of course, the safety was on, so the deputy audibly clicks it off.
Which would be fine, if it weren't a standard Glock 17