Mazo, supposedly the twist of the standard Highwall is better suited for lighter, jacketed bullet smokeless cartridges than BP cartridges using heavier cast lead bullets and BP. They came out with a special version, the BPCR Highwall with slower twist during that era (1995-2001), although you could certainly shoot a BPCR cartridge out of either.
The standard Highwall I have is 1:20 twist
The BPCR Highwall is 1:18 twist.
Of course, for loading and shooting BPCR, one must definitely own a Sharps...would you agree?