but in true sniping, vice sharp-shooting the spotter's job is looking for targets and providing security. The sniper's view of the world is very small and movement is very bad. So in the movies when the sniper is swiveling his weapon around with his scope to his eye, that is not realistic. The spotters scope is magnified but has a much broader field of vision, so he is literally spoting a target and telling the sniper where to look. The spotter doesn't need to be with the sniper at all (remotely located)---but that is usually how it is done.
There are a few different 50 cals--some auto eject and some are bolt action (The first .50cal was a M1 heavy machine gun with a scope and the automatic firing pin lopped out)