PS...wouldn't roll crimped 2 3/4 loads be the answer???
"NO"!!
The load for a nominal 2" roll crimp shell will ordinarily fit the 2 3/4" fold crimp shell with little adjustment needed. The fold crimp 2 3/" shell has a shorter loaded length than a roll crimp one giving more room for the crimp to open without resistence from the cone. This clearence is essential to the use of the longer hull.
This was what was done by Eley & other British makers years ago, as first reported on by Burrard & later by Gough Thomas.
This is essentially what Bell did also so many years later.
The key is, as well put in Roy's last post, the Load must be appropriate for the gun. None of this should ever be taken as a blanket endorsement for firing any & all 2 3/4" shells in a short chambered gun.
