Far Cry 2

The other guide doesn't explain very well what you need to do here. A bandolier is an ammo belt.

Playing through the campaign you will earn diamonds for completing missions and locating the cases around the map. During the tutorial missions you will unlock the weapon shops. When you have approx 15 diamonds go to the weapon shop and use the computer. You can change pages by pressing RB. Buy the Makarov pistol (first page), the accuracy and reliability upgrades (second page) and then the Pistol Belt (third page). This will unlock the achievement. If you don't want to keep these parts/upgrades you can easily save (at the box on the wall in the shop) before purchasing and then revert to your saved game.

Throughout the story you'll earn lots of diamonds. When you get a chance head over to one of the gun icons and enter a gun store. Use the computer opposite to the door to search for weapons. To get this achievement, first you have to select a weapon on the first tab. Note its type after selecting it. Then you want to acquire the accuracy and reliability upgrades for that specific weapon on the next tab. On the final tab, you should select the bandolier for this weapon type. Ex. Assault rifles use an assault webbing and pistols use a pistol belt. Once you make your order, you'll unlock the achievement. Adjacent to the shop is a weapon room where you can access unlimited quantities of your purchased weapons. It's recommended that you set up a good load out as it will help you with the story.