I could link a video, but i think I can make this pretty easy for you...
The best weapon to use is the Kalash with 2x Scope. You should have a few opportunities to get this in previous levels.
On the REGINA level, you will find a railcar on the tracks that you need to push with your car to progress.
Once here equip the Kalash, hold
to use the Military Grade Ammo
Now face away
from the Railcar and hold Up to get moving
Just aim your scope at the tracks and shoot the Nosalis when the come in sets of 3 or 4. They will set on fire in like 2 shots and be no problem. When a few reach your car don't panic & keep shooting the kalash.
After about 4-5 waves you will be clear & achievement unlocked.