I do not worry much about actual shell length, with the two following caveats;
#1 The actul load inside the shell should be compatable with what the gun was intended to use. This lets out modern SAAMI spec shells in pre 20's era guns regardless of chamber length, even 2 3/4" ones.
#2 The end of the loaded shell should not enter the forcing cone. There should be a slight clearence between the end of shell & beginning of cone to allow the crimp to start opening normally.
A fold crimp shell of same fired length will of course have a shorter "Loaded" length than will a roll crimped one. That 2 3/8" 20ga chamber would thus be "Pushing the Limit" even for a fold crimp 2 3/4" shell, but a definate "NoNo" for a 2 3/4" roll crimp shell, even in both cases considering the load itself is proper.
You seldom see this mentioned but if the crimp, prior to opening, enters the cone the constriction results in a "Stronger" crimp. Crimp strength affects pressure.
