I used Power Sword (31-48 slashing damage) with core hover (+20% damage), giving max 57 damage against reinforced walls in Z (56 armor). I tried a couple hundred times and I never got through. I think the chance should be 2 in 18 or (something similar) to destroy the reinforced wall in this case, so I think I have tried enough times to report it as a bug.
Yeah this used to work fine but was broken in Beta 4. I already fixed this while addressing your other damage-related report, but you'll have to wait for Beta 5 to see the changes!
To be clear, I found it back when you reported the overloading damage issue (http://www.gridsagegames.com/forums/index.php?topic=994.0), and already fixed and recorded credit for you a couple weeks ago :P
Walls with resistances do not handle damage properly for now.