Lets Clear Up Some Myths...
1:48 twist rate was
marketed by TC as good for both round ball and conical, but it was not a compromise of any sort. In fact it was very popular many decades before the Minie ball came into use, which was the first widely used conical.
1:48 twist may shoot a conical well..., it may not...it may shoot one or more designs of conicals well, or it may shoot one and only one well. Depth and width of rifling and quality of machining of the rifling have a great deal to do with it. LUCKILY most modern barrels in 1:48 do shoot at least one conical design well.
SLOW twist rates do not necessarily fail to work for conicals. While a 1:60 twist rate may suck for flat based bullets like the TC Maxi-Ball or the Lee REAL..., shallow grooved, 1:78 twist rate works amazingly well in the 3-Band Enfield rifle, known for its sniper like accuracy.
Patched round ball will
today, often shoot well with a heavy charge in a 1:48 barrel, or even a 1:24 twist barrel such as the Pedersoli Jaeger. When the grooves are thin as they often were in hand cut barrels, THEN you get the problems with the ball skipping with a stout load. Meaning something like 90+ grains in a .50 or larger.
So why the slower twist rate in the .54 and other calibers for patched round ball and heavy charges? AH there is more to recoil than the backward movement..., there is torque folks, and fast twist barrels with heavy loads were known as early as the first decade of the 19th century...when the British were developing the Baker Rifle, to
"cause a disagreeable recoil". THAT plus marketing due to the knowledge that in some barrels the ball would skip..., while not realizing that modern equal rifling of lands and grooves being much better for patched round ball and skipping was unlikely.
LD