Gunsmith

Gunsmith is an achievement in Metro Exodus.

Overview
Most weapons in the game have five categories of upgrades that can be installed on them - Stock, Barrel/Mechanism, Sights, Magazine and Gadgets. The only two exceptions are the Ashot, which lacks a Magazine slot, and the Gatling, that has only two upgrade slots with no upgrades available to it. The achievement is received for swapping out the default part in every single slot (category) for a different part that has been collected in the game world as an upgrade for said weapon.

Lists of modifications for every weapon present in the game, along with the location of some of the upgrades, can be found on each individual weapon's wikipage. However, receiving this achievement is not hard, as many upgrade parts can be simply looted from weapons dropped by enemies and they can be installed at any time using the backpack. Even without specifically searching for weapon modifications, the player should have plenty of upgrades in each category available to them in mid to late part of the game, especially for common weapons like the Kalash or the Bastard.

Trivia

 * The background associated with this achievement shows Tokarev modifying a Kalash at the workbench which he set up on Aurora's  passenger carriage. Tokarev can often be seen working with weapons at his workbench in a similar manner in the intermission levels set onboard Aurora.