I purchased a bunch of loads from the maker which were the loads that the barrels were regulated for. But I will also try it with factory sabots and see how they react.
Let's just say that the cost to build the barrels was about half what an RBL professional costs.
If you want, PM me and I can get you in touch with Mr. Hynden directly.

Is he the fellow in Colorado that wrote a book about making a double rifle from a shotgun ?

A sterlingworth would not be the best action for this sort of thing. Brian selected a frame that is very sutable for this sort of thing . Two bites with a greener cross bolt is about as good as it gets. The side clips on the frame help controll the torque from the barrels. Brian will be fireing smokeless loads with heavy slugs. An action with a single bite will shoot loose very quickly. You need at least two bites.

No, that is Ellis Brown. He is still making conversions too. Very expensive as well.