Here's some low pressure 12 gauge loads for vintage guns published by NSSA. They are silent as to hull length, I assume 2 3/4", but if 2.5" hulls are what you want, they could be used with 2.5" hulls by roll crimping or a Hartin crimp on a press.
https://www.nssa-nsca.org/wp-content/uploads/2011/10/ceretto.pdf