RAGE
60 Achievements
1250
32-40h
Wall Hack
Kill 2 enemies with one Railgun Slug shot through a wall
15
How to unlock the Wall Hack achievement in RAGE - Definitive Guide
euclid river
TrueAchievements
TrueAchievements
When you finish the first Scorchers mission (the Hagar Caves), you are given the Nailgun, which will get you both the Railgun and Rebar ammo achievements.
After you've left the caves, head over to shop in the Hagar Settlement (down the central ramp towards the exit of the town), here you can buy Rebar and Railgun ammunition, get both.
Now, head over to the next mission (the Refinery), there is a group of 3 enemies sat around a fire as you enter. First off, save your game, so if you mess up the shot, you can simply reload.
Ease towards the group via the hallway on the right hand side, get out the Nailgun, load up your Railgun slugs and align two of the enemies heads through a wall.
(NOTE: ShootZombies rightly pointed out that it MUST be a WALL, it won't work through any other bits of cover)
It took me 2 tries as you need to make sure the alignment is pretty accurate, as soon as you get them both with the shot through a wall, the achievement will pop!
If you'd like a more visual walkthrough, McoreBE made an excellent video guide below;
.Link: http://www.youtube.com/watch?v=wwJ9IpPRrlQ
Aruwal, Yunder
Introduced into this DLC is a new weapon called the Railgun. You come across the railgun after receiving it from Sarah after completing the Hagar Caves quest. The Railgun has three different ammo types;
- Nails
- Slugs
- Rebar
You can select which type you want to use by selecting 
and using the 
to navigate. With the Slug rounds, the Railgun offers an x-ray scope to view enemies through walls. It's going to be tough to line up two enemies at once (let alone through a wall), a good spot it right in the beginning of the Refinery level. After progressing a short way through, on the right hand side of the large corridor you're in, head down that way and there will be three enemies all talking with each other. You can take the shot through the wall next to the door.
Credit goes to Harry94 for the video below:
Harry94
Note: Equip the Railgun Slugs for the Nailgun by either doing it in the armoury by pressing 
or by holding 
and changing ammo types there. It also has to be a wall, not just any object as confirmed by Terminator.
I highly advise you get this during the 2nd mission "Refinery" as I'm not sure where else you can get it. If you do miss it all you have to do is start a new save file in a new slot, complete the first mission for Dan then you can do the Hagar Caves mission to get the Nailgun which is required for the trophy. As soon as you enter the Refinery, you want to go into the little area next to the curving corridor and aim at the cracked wall. You will see two enemies facing each other, a 3rd will then walk in front and line up with the guy on the right. As soon as they line up fire the gun and it will kill both. The trophy will unlock shortly afterwards.