DwK, I exchanged a few emails with Lee Valley about the Felling axe vs the double bit, and was under the impression than the double bit is actually thicker than the felling axe.
To clarify, when I refer to felling, I am speaking of soft woods like white pine, and of small size, 12" is rare, most is 8-10". The vast majority of homes built here were from felled wood which is why nothing large exists, but even back then 18" was a large tree, which was good because carrying anything bigger is a little difficult.
Double bit axes while common in some areas for felling are almost unknown in others possibly because they may have never been considered, or it could even be a manufacturing problem. Some woodsmen are dead set against them however because of the inherent danger of the second bit.
The narrow bit is a sure sign of a hard wood felling axe though as it directly raises penetration. This may be why they never caught on here as mainly soft woods are cut which can easily still be cleared with wide bits so a more narrow bit would simply require more hits or be problematic with wedging on the softer woods.
Most of the double bit heads I have seen are swampers though not felling patterns and are generally short headed with thick bits. You can generally find them on ebay on occasion, swampers not felling patterns. I am curious as to the performance of a true felling axe of that pattern so I keep an eye out for them, though I don't think they are optimal for the current class of wood here.
-Cliff
