Redding competition shell holders are from .002 to .010 taller than a standard shell holder. Meaning these shell holders do not push the case as far into the die as a standard shell holder. And designed to bump the shoulder back less than a standard shell holder.
The Redding competition shell holders are the same thing as placing a feeler gauge between the shell holder and die to adjust shoulder bump. The main difference with the Redding competition shell holders is you do not need to touch the die and control the amount of shoulder bump by changing the shell holder and still have press cam over.