Yeah, well-made Katanas are nasty sharp and strong. I saw a vid years ago where they shot at one (same set-up) with a .50 MG, captured with a high res camera. It actually took like 3 of those huge slugs to break the blade.
Damn it split a bunch of .50 bullets. The crazy part is that the bullets kept hitting the same part of the blade too, like where it was already chipped, amazing.