I got this achievement in the level after Pollis, where I got the last weapon needed: Kalash 2012. To ensure you get this early, always take a gun you never used from the ground and use it at least once to kill something. You can find the Helsing (rare to find) at the Front Line level on some sandbags (after you climb up from an abandoned area) and you can find a Tihar in many levels. If you use a weapon at least once you are good to get this achievement, but you will also need to buy some weapons.
Note: If you are using another weapon for the other kill achievements, you can leave it on the floor to kill something with a different weapon then get your important weapon back.
Here is a list of the weapons required with locations for the standard versions:
Weaponsmith Achievement Weapons List
Can be looted from almost any dead human enemy or bought in most shops for 15 Military-Grade rounds.
2) Sticky grenade:
* Can be found in weapon caches or bought in most shops for 20 Military-Grade Rounds.
* Not as common in the metro as their nailless counterpart, the regular grenade.
The standard Knife is an unobtainable weapon in Metro 2033, because Artyom uses his own Knife.
4) Throwing Knives
Throwing Knives can be bought in every Metro Station-City that has a Weapons Merchant but because of their reusability that should never be necessary; they can be often found lying around in or around any place where hostile humans are present.
1) Revolver - where to find the standard version:
* Hunter Mission - Free from the red box on the wall when the alarm activates.
* Everywhere else - Found near dead bodies and in holsters of killed enemies.
1) Tihar - where to find the standard version (cannot be bought):
1. Can be found in the level Lost Tunnels, when walking with Bourbon through the tunnels, there is a path going left and there you find two Lurkers eating on a body, near the body, a Tihar can be found.
2. Can be found in the level Dead City 1, in the building with the broken elavator. Fall down the elavator into the room. You'll find a stalker with an unscoped Tihar laying next to him.
3. Can be found in the level Dead City 2, in a dumpster to your right, after meeting up with Bourbon (a use-symbol appears when you look at the lid of the dumpster.).
4. Can be found in a broken railcart in the mission Frontline, and in many other places, usually sticking out.
2) Helsing - where to find the standard version (cannot be bought):
* First one can be found at the near the end of Dead City part 1. Go past the body the demon was feeding on - preferably after dealing with the beast - and head down the stairs and over the wall on the right, and towards a body. Now turn around and walk up the iron bar which comes up to the second level near the bus. Turn around again and jump onto the ledge, there will be a room with a body in it, near it is a Hellsing and several Arrows. Be careful - this area, especially the entrance, is highly radioactive, and you will lose health rapidly and die if you get disorientated in here. It's recommended to pick this one, as it will help greatly with stealth in Dry and commie part of Frontline.
* Another can be found in a room guarded by Nazi soldiers in Frontline, right in front of you as you come up the ladder from the canals after going through the secret passage.
* One in Defense level, in the secret cache with two safes(where you get a Moral Point), near a body.
* In Black Station inside the train after crossing the first bridge and going down the stairs. It is on the seat at one end with a smattering of ammunition, and at the other end is a target with a couple more arrows.
1) Volt driver (new weapon from the DLC) - where to find:
* Lost Tunnels – appears on the bag with the ammunition.
* Armory – appears on the bed with the heavy automatic shotgun.
* Sparta Base – appears on a the pile of boxes to the left of the weapon rack.
1) Duplet (double-barreled shotgun) - where to find:
* Can be found for free in Chase. It's automatically given to the player by Eugine after the quick-time event.
* Other than that it can be found almost everywhere on dead bodies or in stashes even late in the game.
2) Automatic Shotgun (Uboyneg) - where to find:
1. Can be picked up free, from most dead human enemies.
2. Shops - 120 MGR.
3. You can also salvage one from Bourbon's back pack when he leaves it in the Dry (Level) Station's air vent along with extra ammo for it.
3) Heavy Auto Shotgun (new weapon from the DLC) - where to find:
* The first one appears in Armory. After Artyom is forced to flee the Communist Secret Police, and is saved by Andrew the Smith, you will find the weapon, along with a few packs of shotgun shells, waiting for you on the bed, a gift from the smith.
* The second one will appear in Sparta, with the other weapons obtained by Vladimir. If you want it, grab it. Otherwise, enjoy the free shotgun shells.
Assault Rifles & SMGs
1) Kalash - where to find the simple version:
* Can be bought in Armory.
* Can be found for free, first time in Dry. After Bourbon gets captured , turn around 180 degrees and at the end of the tunnel you'll find your promised AK.
2) Kalash 2012 - where to find it:
* You can get it free in Pollis (for sale)
* Available for free at Sparta.
* A number are found on the way to and in D6.
o 2 Are found during "Cave", both near the bodies of tunnel/D6 workers.
o Found in a box inside a small train before the computer control room.
o Found in the lobby of the computer control room by some crates.
o Found inside the computer control room on a shelving unit on the right-hand side of the room.
o Found in a box on a small train before and after the Ameboa pores.
o Found in Biomass on a shelving unit along with a VSV near the ladder (Needs screen-shot conformation)
o Found in ammo box when picking up the 'gift'.
3) VSV - where to find the standard version:
1. Shops - 230 MGR.
2. Ulman will give you one when arriving at Black Station.
3. Another can be found on top of a train car in the Black Station
4. One is used by a Nazi in the final area you fight them in black station.
5. Found in the level Biomass, in D6. Not at the first set of shelves - as you move round towards the ladder to the control room check behind the pillars for the second set of shelves.
4) Bastard - where to find the standard version:
1. Exhibition - Free from Armory.
2. Humans - Free.
IMPORTANT NOTE: Variations and Turret guns do not count towards this achievement. So if you killed something with, say, a standard revolver, you do not need to use a revolver with a scope to get the achievement.
2 - http://metro2033.wikia.com/wiki/Metro_2033_Wiki
Additional Notes: You must get this achievement in one playthrough. You cannot just reload chapters to get it. Also, the Prologue kills do not count.