My father called this technique "Chapell's jar" and as a boy I used it a lot to split the seriously hard firewood logs we have in Australia.
Printable View
That special axe been around for a while, the manufacturer of this axe when it came out a few years ago sent one to the US to test by members of a logging forum.
The axe was tested by many members, the results was pretty much that it worked well on straight grain logs under 10 inches....
I say if you're splitting wood for your fire, you should be looking for a bigger cave.
There's probably more profit in selling axes than using them.