For those struggling with the FMJ challenges I suggest the following. Put together the following build in a spare slot:
Primary: Weapon you're leveling w/Heartbeat Sensor and FMJ
Secondary: Any weapon you're proficient in using (the AA-12 or Akimbo handguns/shotguns)
Equipment: TI
Perk 1: Bling
Perk 2: Cold-Blooded
Perk 3: Ninja
I also suggest adding UAV to your killstreak
Play Domination and wait for Terminal. Now, over by Point A, there is a store across from the hallway that is a frequent choke point in this mode. The hallway is the one with glass windows facing the tarmac on one side and a bookstore on the other. Inside the store you'll be able to stand behind a metal gate (the type that are used in places like malls that pull down from the ceiling and lock into the floor to close up stores), it's a solid wall that prevents you from seeing through it, but with FMJ you will be able to shoot through it easily all the way down the hallway and with the Heartbeat Sensor and UAV in addition to attention to your radar, you won't have to see your targets to draw a bead on them as they try rushing the hallway. Pick anyone off who try to get to your side of the airport through the hallway. Once your clips are empty, switch to your secondary and drop your TI where you stand and then go about your business as usual. Rise and repeat as required.