Joseph Whitworth patented the Hexagonal rifling in 1855. I believe, this patent also includes the bullet rotation of 1 in 20 inches and possibly also mentions this combination in relation with the .451"small bore.
 
Does anyone know where I can find the original text that describes this Whitworth Patent ?

Thank you Bill,
 
As you probably know, Joseph Whitworth has no less than 47 patents on his name. Some about firearms related thinks like barrels scrapers etc. It would be very interesting to have the text of these patents and to see the possible relationship with his investigations in firearms, but it helps to know that he didn't patent the concepts of small-bore combined with fast bullet rotation. By the way you could ask yourself the question if it was possible to get a patent for such a thing.