Here is a bit more definitive information from the book "Mauser Bolt Rifles". The 11mm Mauser cartridge for the original black-powder Mauser Model 71 rifle may have been the forerunner of the cartridges using the concave beveled case head.

LTK did your friends 32-40 cases have any manufacturer's name or other ID on the case or just the 32-40 calibre moniker? The cases may have been made from Mauser A Base basic brass and then stamped 32-40 although would still expect to see a manufacturer's on basic brass e.g. Bertram etc.