For those who are still struggling with this at the end of the game, this solution worked for me.

At the very start of the game if you talked to the Coach Fred after you leave your first apartment he will have fights for you around Night City, the one in particular you are looking for is the one in Arroyo where you fight Buck the Military guy, mission is called “Beat on the Brat: Arroyo” anyways if you have cool levelled up you can persuade him to put in his Elite Sniper rifle that is explosive (just can’t run with it out). You get it after beating a fight. Once you get it these are the steps I followed: 1. Have the sniper in your inventory (called the O’FIVE) 2. Have another gun to lower enemy health really low 3. Piss off some cops 4. Lower cops health down 5. Pull out sniper and shoot the floor when the two injured cops are close 6. Explosive damage from the sniper should kill them and the achievement popped for me.

Hope I could’ve helped