No, you’re correct.
The original ones were chambered in 7.63 mauser which was THE fastest handgun round in the world until the mid 1930s when .357 magnum came out. Broomhandles chambered in 7.63 mauser were popular with gangsters in the 20s and 30s because unlike almost any other handgun, they could shoot through car doors thanks to that high muzzle velocity.
Once WWI started and the Germans adopted the Mauser C96 as their other major military sidearm along with the luger, they had some of them chambered in 9mm luger since they were already geared up to produce lots of ammo in that caliber. To prevent confusion, those had a red “9” on the handle and are called red 9s as a result.
Chinese law in the warlord era in the 20s and 30s did not allow rifles to be imported into the country BUT pistols with shoulder stocks were allowed. The Mauser C96 with a standard shoulder stock was like a carbine and thus they were extremely popular in China with the various warlords and their armies. They even set up their own factories and copied western guns. One of the ones they made was a slightly larger version chambered in .45 caliber. The name for Mauser C96s in China is not Broomhandle, its “Box Cannon”. This especially applies to the ones chambered in .45 caliber.
Thanks for the info. The one I shot was a “Red Nine”. Nice piece of hardware.