Hello Spiral. What a terriffic item!!! Never seen one like it. I own an old beat-up leather one - Turkish I think? Where did you ever find it?
It doesn't look like it, but could it be Egyptian? The reason I ask: You mention the inside diameter being between 11MM and 14MM. From the late 1860's through the late 1880's there was a cartridge identified as a 11MM (.43) Egyptian, used by the Egyptian Government - and others I'm sure. (There was also a 11MM Spanish cartridge). It was a bottle neck cartridge with an 11MM bullet to about 14MM at the base of the case. Hmmmm, maybe your belt was made for that cartridge? Just a thought. If you have access or know an old cartridge collector you could try different samples and see if one fits best. This would give you an approximate time frame your belt was in use. Just an idea. In any case, a great find!!! If you ever decide to part with it...........
Rick.