Herbert,
The information in my earlier posting is based on the US Board of Ordnance recommendations for standardizing rifled arms at the National Armories and Contractors of arms for the US.
The English made P-1853 series (First Pattern through to the Forth Pattern) of Rifle Musket uses a 39 inch barrel. A RoT of 1 -78 equals out to a full one half turn rate for that length. (the American RoT for Rifle Musket is a little faster)
The P-1858 Short Naval Rifle does use a 1 - 48 RoT in a 33 inch barrel. Few of these arms saw service in America during the CW.
The P-1860 Short Infantry Rifle uses the same barrel and RoT. These do see service in some numbers during the ACW.
The 1 - 48 RoT was considered pretty fast for a barrel 33 inches long. It was, however, very accurate for the elongated hollow base Pritchet style bullet.
Late in the production of percussion firearms the British develop a "mid size" Rifle Musket with a 36 inch barrel that also used the 1 - 48 RoT, also considered very accurate.
(For those that don't know, "P" stands for Pattern in England, much like "M" stands for Model here in the US).
My best,
Blair