What's wrong with this sentence?
"Mitchell grabbed the Glock .45-caliber, cocked backed the hammer, and aimed."
Do you see it?
How can you cock back the hammer on a Glock? Glocks don't have hammers--at least, ones that you can see.
I read a similar passage by a very well-known thriller writer and nearly threw the book in the garbage. I couldn't believe what I was reading.
When writing, the smallest details can be picked up by someone if they're familiar with it. I'm no expert in firearms, but I know enough to see the difference.
Sometimes, as they say, the devil is in the details. Put just enough details in the descriptions to make it interesting, yet don't worry about over-describing something to the point where it's a research paper on that particular thing.