Vortex Volley 15G
Caught a projectile shot from a vortex with your own vortex

To employ your Vortex Shield, hold down the Left Bumper (assuming it is your equipped power). To earn this achievement, keep your distance while fighting an enemy Titan and wait until you see an them use their shield as you shoot them. Watch closely to their shield and as soon as it drops, employ yours to catch the bullets/rocket that they've flung back at you.