Beginning today June 3rd, Halo 4 has been given a very large matchmaking update. Weapons have been tweaked, vehicle damage has been changed, even player CMS has been given a boost. Welcome to Halo 4 Turbo.
Everything has been increased or changed to make the balance better for online play. One of the biggest changes is the return of the 4-shot BR. If you want to see the full list, you can find it in the weekly bulletin on Halo Waypoint.