Some how I missed this post and frankly the same question has been on my mind since long before this thread was created.
Why can Maxamet break out pieces of aluminum and brass rods without chipping or breaking, but it can't adequately score a paper and gypsum piece of drywall without breaking farther back on a thicker part of the steel than the part of the blade that is actually in the drywall?
Frankly I dont absolutely know why. After typing this whole post, I think I at least partially know why.
I'll try to delve into this but dont flame me out on this one. I'm going out on a limb to try to begin figuring this out and I do think I have a good answer, or at least a partial answer.
Variables have to be considered:
What we have to remember is that BBB is an expert sharpener and user. He's a knife maker that generally speaking, knows what he's doing and knows what he's talking about. I would expect that you can hand any knife in any steel to BBB, and as long as it's not defective, he'll be able to cut or stab almost anything he wants, and he'll be able to hand the knife back to you in perfect condition after he sharpens it.
Meanwhile I know people who are literally too incompetent to even put the knife in their pocket without breaking the steel clip of my CRKT Caligo, which explained why his old knife was in the condition that it was in.
Those would be the two extreme edges of end-user variables... moving on:
Pushing a knife edge into something, brass for example, loads pressure from the edge to the spine which anything should handle just fine, aside from apex damage. Maxamet is stupid strong at the apex, minus side to side
The quality of the sharpening also matters. Imagine week spots due to inconsistencies at the apex from sharpening.
So then to push strait into brass, no problem, but its not following a strait line. It pushes in, deflects, and pushes out leaving a shallow U-shape in the brass, which can be seen in BBB's video. No doubt that's creating some lateral stress...
What's clear, is that in the way BBB does it, its not creating enough stress to chip, crack, or break Maxamet.
The natural variances in Rockwell hardness from knife to knife matter.... 66 Rockwell verses 69 Rockwell. There's talk of possible 70 HRC Maxamet examples.
Now in contrast with brass:
Push the tip straight into wood really hard without twisting or rocking back and forth. All of that energy spreads through the blade stock and there's no problem. Now continue pushing very hard strait down but angle the blade to the side a little and now the blade will begin to flex. Doing that with a thin flexible fillet knife, minus the high pressure, really underscores the physics of this.
It's the flexing of the blade stock caused by high pressure that's causing the breakage.
Do that with ANY knife steel that's approaching 70HRC and you should expect a catastrophic failure.