One key factor in this is the shell must have clearance for the crimp to open normally i9n order not to get a drastic pressure rise. Loading a 3" shell or even a 3" one for that matter could well have the crimp jammed into the cone which would put resistance on the opening of the crimp. This could cause, & likely would, a much higher rise in Max pressure.
Older SAAMI standards for the 12 gauge chamber gave a minimum length of 2.616" for use with 2 3/4" (2.75") shell. Also listed was a max taper to the cone of 5 per side. This was deemed safe even with a 2 3./4" roll crimp shell. As the "Loaded" length of a roll crimp shell is longer than a fold crimped one there is not as much leeway in chamber length for them. That 5 per side taper in the cone with a chamber end of .798 & standard bore of .729 would give a cone length of .394".
"IF" you have a gun with an Extremely short cone or step then it becomes extremely undesirable to fire any shell with a ""Fired" length longer than the chamber. No gun should "Ever" be fired if the "Loaded" length is longer than the chamber proper, not including the cone.
