MAG

This trophy can be quite hard. The Combat Assault Ribbon requires you to kill 25 enemies with your Assault Rifle. This one is also easy to earn if you have the skills. Before 1.06, the LMG were overpowered compared to ARs, but now it's much more balanced. To get kills even easier, you'll need to flank enemies and attack from behind to get kills. Beware however, your magazine is limited, and your ammo reserve wipes out quickly. You'll need to go back to the supplies several times to get enough ammo.

The Sidearm ribbon is achieved the same way as the Assault Rifle, but the firepower is lower, the magazine is smaller and you have much less ammo. In other words, sidearm weapons totally suck. However, since 1.06, you only need 10 kills in a round (before it was 30!) to get the ribbon. Using the PDW really helps, since you can kill enemies faster with.

For further information: see Ribbon guide (#27, #34).