Rare reverse example - Slow Horses S5.
(Not really spoilers as this happens nearly immediately) - A guy shoots a bunch of people with an assault rifle, gets sniped at the end of his rampage (by someone waiting for him to finish), and I was immediately like, "Well, that's a 5.56mm weapon, and that sniper rifle is 7.62mm, so they'll know he got got by someone else, but they would almost certainly initially assume it was suicide, because it's going to be hard to tell until someone who knows what to look for takes a careful look". "Also that rifle is a high-end military one, no-way the intelligence services believe he just bought it on the black market or something!".
And that's exactly what happened! Good job, writers! Actually did some research and applied some logic, even if you used a kinda-weird name for the FN SCAR.
There were actually several more hyper-specific things which I've not forgotten because they just kept getting them right, which isn't as memorable as getting them wrong.