Used Ironsides to collect 20 rounds of ammo or more in Burial at Sea – Episode 2.
Ironsides is a plasmid that lets you steal bullets from an enemy's gun while they fire and it inserts into your gun (like Borderlands 2 with the Shield that eats bullets). Getting the Ironside will be after you find all the requirements for Suchong’s Research. See "Up and Running" for more information.
If you missed this achievement the first time you can always reload the chapter 'Return to Rapture'. Hold when enemies fire at you.
NOTE: The function to this plasmid doesn’t work that well sometimes they will fire at you and it doesn’t register right or they won’t fire and you waste your eve.
The Police Academy is a good place to farm this achievement where you first get hit by a turret there is a vending machine close for more Salts. Use Ironsides on the turret or enemies works for both, and then keep reloading the checkpoint until you have it. In 1998 mode or Normal mode make sure you aren't full on ammo for your equipped weapon as you can't gain any more.
If you are worried about getting this, right when you get to finks lab, there is a spot with 3 vox and a turret. Empty your cross bow on the vox, and use Ironsides on the turret. Depending on your salt it may take a couple of spawns but you are right at a check point. Rinse and repeat