I'm gonna have to get me that book some day.
Nope not me, it would be about 5/6 oz doubled i don't see why it wouldn't hold cartridge's. and a few silver dollars or even a pistol and knife. Maybe they were made thin so they were comfortable while riding a horse. Plus I don't think using them for a 100 years crossed their minds at all.
I will add that is just one example of a cartridge money belt out of thousands made by different folks, they made things the way they wanted to just like us so leather choice was just that , personal choice, so make yours with whatever leather you want it wont be wrong. however folding thick leather like they were made will be a chore. As i understand it they were one piece folded at the bottom and sewn at the top.