I tried to get this several times and was not having luck, here's what I did in order to get this achievement.
Primary weapon does not matter, no grenades or any other devices i.e. wedge.
Heavy armor with all 11 slots used for ammo for the magnum.
Ammo make sure you use AP.
I equipped the mirror gun, but did not use it.
I saved this as a preset and equipped my squad with the same preset.
I had originally tried to do this mission with the shield but when your squad goes to clear rooms they will use it, which I believe affects the achievement. I had my squad kick and clear any locked doors. Arresting suspects does not affect the achievement. Also one last tip, while it is much slower crouching through the tunnels reduces the noise you make which allowed me to get the drop on several of the enemies.