The British liked to use 1 turn in the barrel. This would give a 32" in your rifle or even faster considering the bore size. They believed the bigger calibers needed faster twists. All evidence to the contrary not withstanding. 48" is a neither this nor that twist, Not all that fast but not all that slow either.

When shooting heavy game they used a lot of powder and the use of too fast twists was the reason the belted ball was developed.
Samuel Baker nearly got killed when he tried a conical in his Elephant rifle (4 0r 6 bore would have too look it up). This was his "devil stopper" and "never failed to floor a charging elephant" but with a conical it lost its ability. This is very bad when hunting Elephant. Or any other dangerous game for that matter.

Bakers books are all downloadable from Google Books. I have not read them yet but downloaded them a couple of days ago.
I would tell you to find a copy of Forsythe's book but they are pretty pricey even the reprint done in the 1970s.
Dan