Chuck, not being one of those who has corresponded directly with shotshell makers, I'd hazard a guess on why they trust the responses given them by the makers of short shells: The makers of short shells would seem to be catering to their clientele, just as are Win/Rem/Fed. And their clientele wants shells which are within the service pressure parameters of 2 1/2" chambered guns. Win/Rem/Fed, on the other hand, are in the business of producing shells, within SAAMI standards, which go "bang" reliably when you pull the trigger, deliver consistent velocity, and--with the exception of some very light loads--have enough push so that an autoloader that hasn't been cleaned since last hunting season will still function.

Horses for courses, as they say.