Both Barrels Achievement in Perfect Dark

Only small guns can be duel wielded

• To dual wield a gun you need to pick up a second gun of the same type of the one your using.
• Only specific gun pickups are duel wields (dropped by guard or placed in level).
• Can be done on co-op

The first dual weapons available are on the first 2 levels:

• Level 1 - Two floors below Cassandra's floor lies a room with a helmeted guard. Kill him and he will drop his Double Falcon 2 (Silenced).
• Level 2 – You need to reach a weapons cache a long ways from the starting point without getting caught. When you begin, quickly close the elevator doors and listen for a guard walking on the metal in front of the elevator. When he’s gone, quickly open the doors and run to the right hallway until you reach a metal door, do not go through. Wait for the yellow hover bot to come and open the secret door to the left of the metal door. Run in and turn right. Break the glass panels on the side with your fists and jump down. Here is the tough part. Peek through the right corner here and make sure there are no guards. Run down the hall and into a small room with a computer inside. Activate the computer and you will earn duel CMP150s.

When you shoot your first enemy with duel weapons equipped the achievement will pop!