I still don't see it. There are sci-fi guns like blasters, historical guns like flintlocks, and there are guns used in superhero sets, but nothing for Lego City or any other set that claims to represent real life.
Admittedly a revolver and not a semi-auto, and I don't know if it's from a current or recently discontinued set. But it's definitely from a modern set.
edit: link to the specific piece: https://www.bricklink.com/v2/catalog/catalogitem.page?P=1356...
The BrickLink page lists the revolver as part of a bunch of western and cavalry sets, that is, historical sets. Click "Item Appears In: 7 Sets" to the right.