Can't give much help, but I will offer this: My 1940 Shooter's Bible shows that the "high brass" 28ga loads back then were 2 7/8" in length. Super-X, Remington Nitro Express, and Peters High Velocity all list that length for their 28ga shells. The other option, in the less expensive lines of shotshells, was a 2 1/2" 28ga containing 5/8 oz shot. Not sure when 2 3/4" was finally established as the standard 28ga length, but it would appear to have happened after WWII.