Metro 2033

EDIT: due recent comments, i'll edit the solution once again to try improve it.

I personally tried different methods and this is by far the easiest place and quickest way i found to get this because of this reasons:
1) you have infinite amount of enemies coming
2) the mount is stationary (unlike trolley combat which is moving) and the enemies keep coming from the same spots all the time, making the aiming much easier
3) if you fail and you have to reload checkpoint, you don't have to repeat half of a level, you can go straight away to try again.

so, this is what to do:
load up CURSED (on easy mode), go to Khan so he tells you to go for the explosives and blow up the tunnel.
But don't do that. Instead stick close to Khan and use the mounted machine gun.

Now the thing is: it has limited ammo. exactly 50 bullets (credit to MonkyCMonkeyDo for confirming this), however every enemy just needs 1-2 hits to die so you should be more than fine.

Don't try to aim around from left to right "chasing" the enemies. Just point your crosshair to one of the entrances from the left tunnel where the enemies are coming from (or the right tunnel if the AI is in middle of your sight) and wait for the enemies to come and shoot CAREFULLY when they are on the corner about to enter the main tunnel. 1-2 shots per enemy. Use LT to zoom in and don't move your aim too much.

Due recent comments i want to stress again to NOT aim around like crazy and focus your sight to one of the side tunnels and you'll see the enemies coming that way. Aim at the head or torso if possible and wait for enemies to come and just shoot them when they go around the corner before your AI partners kill them. AI is usually focused killing stuff in the main tunnel.

ANTI-EDIT:
following parragraph was here since i made the solution, but i can NOT encourage to do this, it seems to confuse people who is reading this solution, but it might be useful for some people so i leave it here:
Sometimes 2-3 will come from the front. If you get a quick clear shot on those when they are very close, by all means: do so. Chances are they are "softened up" by your allies already and will die with just one shot.

You'll get the chievo in no time. If you don't get it first try, just reload the last savepoint and try again.

EDIT: i'd appretiate feedback from everyone, specially negative voters to know what's wrong with the solution.

Got this one while playing through the levels "Front Lines" and "Trolley Combat". As you begin the level "Front Lines" there is a stationary machine gun a few feet away from the fascist who says "join me in a song".

Kill him and his buddies and then man the machine gun and kill as many enemies as you can on the other side. When you think you have 5-7 kills just finish the level and proceed to "Trolley Combat". I got the achievement on the last post of enemies before taking out the Panzer. If you don't get the achievement by the time you reach the last post of enemies, reload the checkpoint and try again. Took me a couple of tries.

Play "cursed" with "Ranger Easy" difficulty. You only need 1 shot to kill a nosalite on ranger easy. Go to the mounted machine gun wait for the waves to come.

There will come 2 nosalites from the first opening to the left, then with the next wave, 2 nosalites come from the second opening from the left. Use only 1 shot to kill 1 nosalite, and repeat. The machine gun has about 50 bullets and I think the achievement popped for me after shooting 15-18 nosalites on my second try.

Cursed station: Avoid wasting ammo when shooting the nosalies, should get you plenty of kills.

Frontline: You can kill a few guys at the the first machine gun before crossing the bridge to the other side, just dont shoot the ones on the other side before reaching the machine gun.

trolley combat: Quite self explanatory, just get as many kills as you can before you reach the end of the level.

The two easiest locations in the game to earn this one are Cursed Station and while escaping from the Nazis on the trolley. Otherwise mounted machine guns are never in a good spot to take out enemies.

FRONTLINES N TROLLEY COMBAT
i had some troubles getting this, the solutions above works but i wanna explain what i did to get the chevo... hope this helps

1. at the beginning kill all the enemies on the railcart in front of u n keep straight clearing this area without shooting the ones across the left side bridge until u see the stationay gun

2. when u manage the gun there will 2 easy kills that u can spot with no prob

3. after doing that i did not have a clear shot for the other enemies so what i did was cross the bridge get they attention WITHOUT KILLING n then go back to the stationary gun, they will start walking around n u will have some clear shots, just do it in rounds so u dont waste the ammo... by this time u will have 4-5 kills

4. then just finish the level until u get to TROLLEY COMBAT doesnt matter if u die on ur way to finish frontlines

5. now one in the cart when u knock the horn n pass the gate, aim behind u, u should see a soldier standing n then before u can start shooting another soldier will get close... this way when u reload ur checkpoint u will be aimming at those guys n u can get 2 or 3 kills (mostly times i got 2 kills the first soldier n the guy who is in front of the cart asking ur name, u will see him when the cart starts moving)

6. once in move keep aim behind shot in rounds at the cart to ur right when u can see it, DO NOT SPAWN AMMO or u will heat the gun n u dont wanna do that for the next step

7. now focus on the cart behind u, u have to kill em quickly, if u do another cart will show up behinf u, if u dont u will lost 2 kills so keep that in mind, u better wanna load ur checkpoint if u miss the second cart... u should have about 10-12 kills

8. after this third cart aim in front of u (that means forward towards the direction of the cart) to ur left, u will see a soldier running, kill him n then there on the left u will see 2 other soldiers, n another at the end of this station near the roadblock ahead, then shot the roadblock n continue
(i have to mention the game wont continue until u shot the roadblock but the damage taken from the carts n the 4 guys in this area may get u killed so try take em as fast as u can)

9. keep aimmimg in front of the cart to the left, u will see some flashlights up ahead... when i kill 1 slodier here the chevo pop but theres a couple more soldiers there to kill, they r in plain sight n u may get more than 1 kill if needed but if u follow this steps u shouldnt have any problems

if u didn get the chevo here load checkpoint n keep trying, i know is hard to handle those stationary guns but dont give up


This is my first solution, some feedback would be nice XD

I figured I'd throw my two cents in since this achievement gave me some issues.

I'll start by saying that all the above guides are great and if you were able to obtain the achievement without much issue then congrats.

However, if you're having difficulty getting this achievement (like I did). I would recommend following this guide.

I'll also mention that this guide is a modified version of Phoenix C64's guide, so all credit goes to him. I just figured out a way to make it somewhat easier.

Load up the mission "Cursed" on Easy difficulty.

Once the level starts, follow Khan to his friends and listen to your orders. Now, rather than following them just mount the machine gun nearby.

Now then, your machine gun only has 50 bullets and it takes 1-3 shots to kill an enemy, so every shot counts. The downside, your teammates are a bunch of dirty kill-stealers and will take almost every one of your kills. This is kind of a big deal, since if you want this achievement as early as possible you'll need to get all 15 kills here. That and the fact that reloading the last checkpoint won't add to your kill count doesn't help either.

What you're going to do is simple: you're going to give your teammates a bit of their own medicine.

First you'll wait. The Nosalises will attack you and your allies but don't worry, you'll live. Stay on the machine gun and let this go on for a few waves, your allies are invincible and have infinite ammo so they can hold out with no issues.

As this continues, you're going to notice that one of your allies (usually Khan since he was standing away from everyone to give you your orders) will slowly be pushed away from the barricades with each wave.

This is what you've been waiting for: Live bait.

With Khan now away from the barricades the Nosalises will attack him and then move on to you and your team with one Nosalis choosing to play with Khan. The other Nosalises will eventually be killed by your team so ignore them.

The one playing with Khan however, will survive longer since your teammates can't tell them apart and will usually shoot Khan instead. With Khan taking fire and getting hit by the Nosalis he can't fight back, so this is the kill you'll scoop up. This Nosalis will also usually be killed in one shot, since your teammates probably got a hit or two in.

Now just rinse and repeat.

I will warn you that occasionally your teammates will just completely destroy the Nosalis waves, so just be patient and kill the one that plays with Khan when you have a clear shot.

Another thing to watch out for is that if Khan goes too far away it is less likely a Nosalis will want to play with him. They still will though, it'll just take longer and happen further away so zoom in if you have to.

The furthest Khan went for me was in between the first and second tunnel and at that point only one Nosalis from every two waves would play with him.

In the beginning, it is possible for the "Bait" to get stuck on one of the barricades at the start. If after a few Nosalises waves pass and he doesn't move, I would recommend reloading the last checkpoint.

Also if one of the AI gets in your field of view, either wait for a wave or two to pass for them to move or just reload to last checkpoint if it's early enough.

On Easy difficulty you should survive being stationary on the machine gun. There were a few times that I came close to death, but I was always saved by the AI and usually went back to full health during the lull in between waves.

This is just a helpful addition to Phoenix C64's method on "Cursed". Aim for the first tunnel on the left, just below the shadow of the hanging cans. As soon as anything moves, just let loose one shot.

On easy mode, this will be a one shot kill as where I told you to aim would be a headshot.

Everything already posted is great, but I realized a helpful tip and didn't see it anywhere: whenever you hop on a turret, go into game controls and set both sensitivities to zero. Gives you a bit more control. Just don't forget to change it back after.