1.Find a wall that perhaps you can shoot through or if you go up close to it, there is now space between you and the wall.
2.Even if it's a straight wall,try and find part of it that sticks out or looks like a corner.These "cracks" in the walls are hard to find and you will most likely find them in on rocks.
3.Now just keep pushing towards that crack and jumping repeatedly,until part of you goes through the wall.This will not work on all cracks but if you find just the right one and keep on jumping,than you could find a wall breach.
4.Not all wall breaches go exactly like that.The Old Roundhouse one had no cracks at all.It was simply just a soft spot.If you get lucky, than maybe you can find one and wall breach through it.Also sometimes you have to go prone to wall breach.Once your prone,find a spot that goes into the wall a little bit.Now keep on rubbing your self against that spot and keep going into it then out and you might find a wall breach.
Notice how that part sticks out of the rock and he jumps all around and into it.
Also,if you know you can wall breach through something but just cant get through it, try to sprint back and forth against the wall and that might also get you under the map.
Enjoy finding Wall Breaches!^^