Singularity

You will find this gun very early on in the game. 30 kills is simple, with this shotgun. Just remember if you die, the kills still count. Of course, if you want this a little bit faster you could always upgrade the shotgun.

I did find a nice place to grind this.
Very close to the start of Mission 2, you'll see one of the devices which allows you to change your weapons.
Make sure you have the Volk S4 Shotgun in one of your two weapon slots.

Shortly after this, you'll go through a set of blue doors, and you'll see a Chrono-Echo. You'll then go up the stairs. You can go to the right for some ammo, or to the left, where you see your first Zek of the game. Fire some shots at it and it will teleport away. You can then go down some stairs, where you can get some Centurion pistol ammo on one of the boxes. There's also an Audio Recording in this room.

You will now drop down into the next room, and get a checkpoint. This is important! As you move forward into this room, a Zek (a short, bulbous-headed, light-blue-coloured enemy) will appear. This is brilliant, because you've just had a checkpoint. Kill it with your shotgun (it should only take one shell), and reload the checkpoint. Keep reloading the checkpoint and killing the Zek for the achievement to pop. If, like me, you switched from pistol to shotgun when you first came across the shotgun in Mission 1, you probably will only have to do this 10-15 times, dependant on how many enemies you've killed with the shotgun so far in the game.

- Dwaggie