What kind of Helmet is this?

I recently acquired this helmet at auction where it was described as "Bulgarian". Initial WWII research took me to the Bulgarian M36, and even an early WWII M36, but with the heavy side lugs, I looked at WWI. The closest I can find is the rare "Berndorf", but even that has the suggestion of a visor, and this helmet is straight all the way around. The crown is also more spherical than the Berndorf.
The WWI style side lugs seem to be toward the rear of the helmet, but this could still be the front. I've positioned the helmet assuming a small insignia clip welded to the helmet would be toward the front. Unlike French "Adrians", that attach through two holes, if this helmet held a badge, it would have had a tab that would slide vertically through a single slot.
Lastly, this example has no heat stamp or serial numbers anywhere on it or along the rim. The rim is straight without any crimp, and the liner is a standard foreign style leather (missing) held by the metal band and split rivets.
If anyone has seen one of these, please let me know. I'm stumped!