i've seen illustrations of them with concave, straight, convex and multi-pointed shapes, rectangular, etc. googling 'bullova axe' & selecting the images will bring up a bewildering variety, like this image i found googling:
not sure how that was intended to be used either, looks like it might stick in the target...the more usual moustache ones
were noted on one indian blog as being notched in the middle to fit an intended victims neck, tho this seems unlikely to me. not a lot out on the ol' internet...
i read somewhere that the earlier ones were made in two parts, the blade part being riveted to the neck of the eye part, the later ones forged in one piece. in mine it appears the eye & neck were one piece, and the blade and it's neck piece were inserted and hammer forged together, you can see the layers in the following:
