Peterson Cartridge Company is making the brass for Superior Shooting Systems.

The 33XC (.338), 37XC (.375), and 41XC (.416) are based off of a .580� bolt head

The 33XC is the parent case for the 37XC and 41XC. Meaning the brass used for the 33XC is the same brass that is used for the 37XC and 41XC. The brass for the 37XC and 41XC is simply necked up to .375 for the 37XC and necked up to .416 for the 41XC. The brass will still say 33XC on the headstamp.