I just ran a stick of Win.32-20 into a .30C die and measured against my 32-20 once fire in a 32-20 Colt's Army Spl.
It is pretty hard to find much difference. Now, just so no-one gets the wrong idea, this DOES NOT mean I will ever put a .30C into a 32-20 chambered gun!!! From these measurements the rimless .30C might actually fit, then somebody would be tempted to pull the trigger.
You know......." it dropped in, I was there, it was there, so I.............".