The M24 is the first sniper available to you in Operation 7. It is a bolt action, composite body sniper rifle used by the US military and police forces. It was, in essence, responsible for the creation of the Dragunov SVD. In-game, the rifle has a low relative accuracy (92-93%) and seems to degrade faster than the AWM.
It is one of the most common sniper rifles in the game. It may not have great firepower (incapable of taking down an enemy in one hit anywhere, but no rifle can do that unless it's the AWM with JHP rounds), but it is basic and pretty easy to use. Sure, it will take two shots, but make sure you're in a good position (mainly somewhere where's there's cover) and and you can easily take down your enemies.
This bolt-action rifle, though common, is basic and is not recommended by new sniper users. It is best off (but not required) that they stick with a scoped automatic weapon until they can rank up and get an easier-to-use rifle.