I’m not gonna try and make this the longest guide you’ve ever had to unnecessarily read, because doing this farm isn’t complicated whatsoever.
Before I say anything else, remember that you NEED to be using the weapon with the Ammo type you want to grind for in order for this to work. So, if you’re farming for 5.56, you’ll want to be using any rifle that fire that specific type of ammo.
Your first job is to simply complete a Daily Ops, hitting absolutely EVERY single enemy you possibly can along the way. If you don’t at least deal a bit of damage to the enemies, they often times won’t drop any loot for you.
Once you’ve complete the daily ops, you’ll notice that, unlike other enemies in the game, all THESE enemies you’ve killed have dropped a good amount of Ammo, specifically the ammo you used to kill them! It can vary how much Ammo they drop, sometimes they’ll only drop a couple, whereas others can drop up to (as high as I’ve personally seen) 24 rounds! After you’ve killed a solid probably 50-100 enemies in the Daily Ops, that number racks up REAL quick.