Why the brass hulls ?

Your friend does know that in a SxS there's the possibility of a the load shifting in an un-crimped hull from the recoil of the other barrel.

It's really easy and simple to load 10 ga. plastic hulls with a roll crimper and a short piece of 5/8" dowel rod or just get some gauge mates and shoot low pressure 12 ga. ammo out of it.