are rcbs and redding shell holders interchangeable?
If you mean can they be both be used in a Redding Big Boss, then yes. But the numbers on the RCBS are not always the same number as is on the Redding... i.e: A Redding #1 is the same as the RCBS 3 & 11. A Redding 2 is the same as an RCBS 2.