Pedersoli's SxS rifle barrels are joined together in a jig. They are not regulated in any way. Regulation would mean shooting them and adjusting the barrels using wedges, etc.
They do NOT do that.
The 80 gr. Max load is a litigation relief designation, pure and simple.
I would expect roughly 1,400fps. to 1,450fps. from a 150gr.2F load in a 12 bore with 30" tubes.
Breech pressure should be in the 8,000psi range. That is just a guess.