For this Achievement/Trophy you can do it on the mission
Takedown on
Recruit difficulty. You’re allowed to shoot just make sure you don’t reload either by pressing the reload button or having no ammo in your clip. The flash bangs are really good for this.
The first part of the mission is fairly straight forward so shoot the guy in the leg as normal. After this once you drop down into the favela area stick to the right side to avoid most of the enemies.
Then follow the dirt path along until you get to the end of the road then throw a flash bang to run past the enemies. Continue following the path and eventually you’ll see some houses on the left side for you to take cover in if you need to. Keep making your way through the level by using your flash bangs to distract the enemies. Eventually you’ll come across some white stairs after taking a left turn, go up those stairs and throw the flash bang at the three enemies that spawn in front of you.
If you haven’t reloaded either weapon, you’ll get the achievement/trophy in the cutscene.
If you're still struggling, feel free to use this as a reference.
Hope this helped, thanks again.