MAG

The Combat Machine Gun Ribbon is earned when you kill 25 people with a Machine Gun in one round, when the Combat Fragger Ribbon is awarded when you kill 10 people with frag grenades. The Machine Gun have the same power as assault rifles, but they have a much larger magazine, but also a bigger recoil and less precision. But the bodycount will increase quite quickly, especially if you get every upgrade in the skill tree, and you will get the 25 kills quite easily.

The Fragger Ribbon is more difficult to earn. You can only carry 2 grenades at a time, and sometimes the grenade throw is quite unpredictable. You'll need to know how to throw your grenade exactly where you want it. A good tactic is to throw grenades into areas where you are sure there are plenty of enemies, like bunkers, or lettered objectives. After getting each ribbon 5 times, the trophy will pop. Grenade launcher kills doesn't count!

For further information: see Ribbon guide (#28, #30).