How do you kill the big armored dude in madness project nexus

You have to punch him rapidly(melee weapons don't work).A few cracks will appear on his helmet,then a more and finally it will come off.Then you have to shoot his head.I killed two of them in many waves in the arena but not in the campaign yet.
But believe me!It works!

Other Random Guy:Melee weapons don't work,but Sanford's hook does.Try it but he will keep shoving you so it will be hard.Good Luck