Here are a couple of pages from the January 2, 1942, Western Cartridge Co. price list. Note all the 12-gauge Xpert field loads on page 3 are all in 2 5/8 inch cases, but the Xpert Trap and Skeet loads on page 4 are in 2 3/4 inch cases --
The Trap Loads being in 2 3/4 inch cases is not because of the new Super-Seal crimp, they were all 2 3/4 inch roll-crimped cases back in the 1936 price list, well before the Super-Seal crimp came out. Actually their earlier Trap Loads in the FIELD or RECORD cases were in 2 3/4 inch, or longer cases, as far back as my collection of Western Cartridge Co. paper goes.