some very niche Special Forces stuff. Basically, in urban enviroments, you won't necessarily be dealing with super long ranges, and there's issues with concealability - if you need to deploy a rifle at a window, obviously the barrel will be poking out and give away your position. So, in certain very specific situations, it makes sense to use a revolver as an improvised sniper weapon.

The Forgotten Weapons video that Zoryn posted goes into more depth

Oh boy my time to shine! Forgotten Weapons has a video on this exact set up

https://www.youtube.com/watch?v=P1zEUGck8NE