You can get the map needed for this achievement from GameBanana[gamebanana.com]. Once you have downloaded it, install it by following these steps:

1. Go to the Counter-Strike:Source installation folder. This is usually C:\Program Files (x86)\Steam\steamapps\common\Counter-Strike Source
2. Copy the 'maps' and 'materials' folders into the 'cstrike' folder.
3. The map is now ready for use.

If you don't know how to enable the console, follow these steps:

1. Start the game.
2. Click 'Options.'
3. Click 'Advanced.'
4. Ensure the box next to 'Enable developer console' has a tick in it.
5. Click 'OK.'

The tilde key (`) can be found next to the 1 key at the top of your keyboard. It is usually under Escape.

1. Start the map and join the Terrorist team. You might want to start without bots, or enable 'Bots join after a player joins.'
2. Open the console and run the following commands:

• mp_limitteams 0
  
• mp_autoteambalance 0
  
• bot_knives_only 1
  
• bot_join_team ct
  
• bot_quota 59
  
• mp_startmoney 16000

3. The bots will spawn above the ground, meaning they will take about 85 points of fall damage.
4. Buy the weapon you want the kill achievement for and blast away; if you need achievements for the CT weapons, they can be found behind you as you spawn, along with a free HE Grenade.
5. Start shooting.
6. Repeat step 5 until all the bots are dead.
7. Repeat step 6 until you get the achievements.

1. The bots will run backwards on round start, which may cause framerate issues if a high number of them are used. Once you kill one, they'll stop moving to look at you.
2. You can get knife kills without the bots being able to stab you; stand close to the wall and use the range of your melee attack to your advantage.
3. The Terrorist team only has one spawnpoint.

It is also possible to earn other achievements using this map; they include, but are not limited to:

• Variety Hour
  
• Battle Sight Zero
  
• Repeat Offender
  
• Decimator
  
• Overkill
  
• Command and Control
  
• Ten Angry Men
  
• Blind Ambition (if you buy Flashbangs)
  
• Blind Fury
  
• Spray and Pray
  
• Friendly Firearms
  
• Hip Shot
  
• Three the Hard Way
  
• Ammo Conservation
  
• Happy Camper
  
• The Cleaner
  
• Clean Sweep (possibly)
  
• The Unstoppable Force
  
• Head Shred Redemption
  
• Blitzkrieg (if you use the right weapon)
  
• Black Bag Operation
  
• The Frugal Beret

With this map, I was able to get all of the weapon achievements in a couple of hours.

If this guide helped you at all, I'd appreciate it if you upvoted and/or favourited it.

I'm not really all that interested in Steam Points, but if you want to give me an award, that's entirely up to you.