When the SAAMI specification started in the mid-1920's, the 12ga expanded hull length was standardized at 2 5/8 to 2 3/4" for shells marked 2 3/4". Before the SAAMI ( Small Arms and Ammunition Manufacturer's Institute) standards, the various cartridge manufacturers had varying lengths. Dave Noreen has old ammunition catalogs and he could be specific.
That's why today, you can look at many expanded hulls and they are less than 2 3/4". Win AA's are typically 2 5/8". Not that it really matters.
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