Unlock all weapons by hitting every Convoy.

Unlock all weapons by hitting every Convoy. After you've hit two convoys, you'll unlock an RPG that makes the ambushes even easier. Simply keep accepting missions at the weapons dealer until they have no more left. There are four missions in the north and four more in the south. Once you've unlocked all the weapons, this achievement will unlock. You don't actually have to purchase all the weapons for this achievement.