Resident Evil Revelations 2

Near the end of Barry's story you come to a gate that is locked with chains. This area has a couple of Revenants, but only 2 have a weapon for an arm which is what you are looking for.

Run up to the gate and interact with it. A Revenant will then break through the fence behind you. Try only shooting it in the arm or chest to destroy the weapon that is attached. Don't kill it early by shooting the red bubble before getting the weapon off.

After you're done with the first, run to the house next to the crane and find the second one that is hiding in one of the back rooms. You can now reload the checkpoint and repeat this. Your ammo will be filled up again.

This achievment most likely needs some farming. I had almost everything done and played through all of the episodes multiple times and still only had 20% of the achievement.

I think the fastest way to get it is in Barry's chapter of episode 2. In that episode, you don't need to play till the end of it. If you rush through the first part of the level (roughly 10min in the episode) you'll come to the spot at which you separated from the male character in Claire's episode. Go through the blue door inside the building and you'll find yourself at a staircase. Go all the way down and through the door. You' ll find an enemy with a weapon arm right in front of you. The neat thing about this method is, that your checkpoint will be right in front of this room. That will make it incredibly fast and easy for you to get the 30 kills. I recommend using the Magnum for this. Don't worry about ammo, since you are going to abuse the checkpoints. Aim at its arm, slightly above the weapon part. You should destroy it with one or two shots. Rinse and repeat!

(Video credit: Nathan Summers)

Hope this helps!
Any improvements? Please let me know in the comments below!