Hello:
I have been told by Romano that, over many years, he's encountered three A-sport, 56-50 Spencer twists.
I don't know all, but one was 24".
From the experiences of two A-S Spencer owners, even the Chiappa Warranty Center in Dayton, OH, that is supposed to be able to match serial number to production parts variations/specifications, has not been much help.
Taylor's only knows about the current stuff they handle. Taylor's Winchester VA techy's have been extremely professional and caring, but these sort of questions are referred to Dayton.
Frankly, it is not easy to measure twist accurately via tight patch and I have been off as much as an inch or two with many barrels. No one has been able to tell me WHY most CW era twists are in even, whole numbers instead of either odd numbers or fractions. The Merrill breechloader seems to be the only one with a partial inch twist, per specifications.
Burnside '65's in 56-50 had 24" and were reportedly quite accurate.
Still, 36" in Douglas' 56-50 barrel blanks (used on some repro's, not A-Sports') and 32" in Romano's barrels or his Spencer liners works very well with a 310 - 315gr bullet ahead of 35gr 3Fg.
That UTUBE vid of the fellow gong shooting from the bench in the wind remains chillingly inspiring.
One w smokeless, one with black. Bang ... Clang! Shot-after-shot! Have to love it.
All the best,
El Supremo/Kevin Tinny