3rd Edition of Graeme Wright's book "Shooting The British Double Rifle" has an entire chapter (14) devoted to Paradox guns with suitable loads for the 12 Bore with Paradox type bullets. Blue Dot & Unique loads published.
Remember, it is essentially a rifled shotgun so typical shotgun powders are indicated, don't worry about Unique.

If ….the big "if"….you pursue black powder loads just be sure to use a black powder compatible lube. I personally recommend SPG.
Smokeless loads? Yes, Lee Alox or any other lube will be fine.
- Mike