Steam Discussion...
How I finally did this was, after doing a YouTube search for "SGW Contracts - Arakcheyev 5 kills with one explosion", I tried each of the methods from the listed results and I found the easiest way for me to get this challenge was when the bounty became available for Pvt. Ilya Stovetov. He's the one at the west end of the map. Take out all the closest enemy that you first run across, then sneak out on the ice, up to the group where the bounty is, as close as you can without being spotted. Wait for the group to get together and throw a frag grenade into the bunch. The only trouble with this method is that, once you've collected this bounty, it's up to chance if it will be available to you the next time you go back in the map.

The other methods were frustratingly difficult for me. To get the precise timing required so that 5 enemy will be killed seemed nearly impossible. You have to keep repeating it until you finally just get lucky. I'm not a fan of 'trial and error' gaming.

I finally got it on the helo pad at the fortress. After several tries I was able to get 5. I dont mind solving puzzles, but it should be a repeatable objective rather than a random possibility.

I believe I got this by attracting them to an explosive barrel and shooting it.

Hope no one minds the necro as a lot of players just got the game. The tip with the heli pad was great, but it doesn't "just work", so here is a step-by-step that works 100%:
1. I used B95 Chris with explosive ammo.
2. Quick travel to fortress, climb up to sniper position, but ignore him. Instead take the path to the left leading down and stop by the red ropes hanging down.
3. Don't zoom in yet, but take note of the far left soldier. We need him to be in the blast radius.
4. Make sure explosive shells are loaded and shoot a warning shot onto the heli pad, roundabout where that red navigation light is between you and the helicopter. Moments later everyone starts fleeing.
5. While that happens, keep the scope view up and aim at the exposed rocket pod. Pull the trigger the moment you see the far left soldier cross your sights and disappear behind the helicopter. This kills 3 light soldiers, Alichanowa and her double.

引用自 Streuwinkel：

Hope no one minds the necro as a lot of players just got the game. The tip with the heli pad was great, but it doesn't "just work", so here is a step-by-step that works 100%:
1. I used B95 Chris with explosive ammo.
2. Quick travel to fortress, climb up to sniper position, but ignore him. Instead take the path to the left leading down and stop by the red ropes hanging down.
3. Don't zoom in yet, but take note of the far left soldier. We need him to be in the blast radius.
4. Make sure explosive shells are loaded and shoot a warning shot onto the heli pad, roundabout where that red navigation light is between you and the helicopter. Moments later everyone starts fleeing.
5. While that happens, keep the scope view up and aim at the exposed rocket pod. Pull the trigger the moment you see the far left soldier cross your sights and disappear behind the helicopter. This kills 3 light soldiers, Alichanowa and her double.

That is very good tip man, thank you. I simply used 2 AP bullets, does the job just fine.

引用自 Streuwinkel：

Hope no one minds the necro as a lot of players just got the game. The tip with the heli pad was great, but it doesn't "just work", so here is a step-by-step that works 100%:
1. I used B95 Chris with explosive ammo.
2. Quick travel to fortress, climb up to sniper position, but ignore him. Instead take the path to the left leading down and stop by the red ropes hanging down.
3. Don't zoom in yet, but take note of the far left soldier. We need him to be in the blast radius.
4. Make sure explosive shells are loaded and shoot a warning shot onto the heli pad, roundabout where that red navigation light is between you and the helicopter. Moments later everyone starts fleeing.
5. While that happens, keep the scope view up and aim at the exposed rocket pod. Pull the trigger the moment you see the far left soldier cross your sights and disappear behind the helicopter. This kills 3 light soldiers, Alichanowa and her double.

is there any kind of video out there that demonstrates this?

Thanks for the tip here. I have attempted the heli pad method and got five kills with the heli explosion fairly easily. BUT the game doesn't register it :( I clearly count five bodies, three normal soldiers plus two ladies, excluding the heavy armor soldier who withstands the explosion. Wtf is wrong with this challenge.

引用自 Raptor_Gunner13：

引用自 Streuwinkel：

Hope no one minds the necro as a lot of players just got the game. The tip with the heli pad was great, but it doesn't "just work", so here is a step-by-step that works 100%:
1. I used B95 Chris with explosive ammo.
2. Quick travel to fortress, climb up to sniper position, but ignore him. Instead take the path to the left leading down and stop by the red ropes hanging down.
3. Don't zoom in yet, but take note of the far left soldier. We need him to be in the blast radius.
4. Make sure explosive shells are loaded and shoot a warning shot onto the heli pad, roundabout where that red navigation light is between you and the helicopter. Moments later everyone starts fleeing.
5. While that happens, keep the scope view up and aim at the exposed rocket pod. Pull the trigger the moment you see the far left soldier cross your sights and disappear behind the helicopter. This kills 3 light soldiers, Alichanowa and her double.

is there any kind of video out there that demonstrates this?

Just completed it and here is video: https://youtu.be/hUGjc-mnv-8
Sorry its pretty ♥♥♥♥♥♥ video :P
Didn't think i get it with first try(with this method) and almost missed video with GFE.

-e-
and thanks as mentioned got this with first try, tried few times from sniper location and didn't work.