I don't know about Rice, but I built a fowler using a Colerain 16 gauge octagon-to-round barrel, I think their Griffin profile, a little over a year ago. It has a wedding band between the octagon and round segments. I went with the 16 gauge because the external dimensions are the same as their 20 gauge, but with less metal, hence lighter. It's a nice barrel, cylinder bored, and I was happy with it. TOW lists the dimensions and weights of the Colerain barrels in their catalog and online. They don't describe any Rice smoothbore barrels, only rifled. You'd need to call Rice.
Gregg