Interesting axe, Tim. I have never seen one like this before.
In your last post, you show a Momvu sickle knife. In his book 'The Sickle Weapons' (2000), the author, Jan Elsen, gives an oversight of the different types of sickle weapons found in Central East Africa. It's possible that your axe fits in this category.
These are the prototypes (according to the author) from which the Mangbetu and also the Momvu knives evolved.
I scanned the pages (I hope it's clear enough) :
Here's a sickle knife I recently found on ebay and that fits into this category.
