ORIGINAL: Vapodog
I've always thought it was a way for Winchester to use the barrels intended for the .30-30 that turned out oversize when the drilling was complete. Instead of scrapping them they reamed them to .32 caliber and rifled them. I really don't have a clue why anyone would bring out a round almost identical to an existing one in the same bullet weight and the same rifle with the same energy level.
Ballistically there's nothing special about the .32 Winchester special.
NOT EXACTLY! .32 Special barrels had .32/40 bore dimensions and slow 1/16" twist ON PURPOPSE!! It was a way for Winchester to offer .30/30 equivalent ballistics in the M94 rifle, using barrels with the same bore and rifling as the .32/40 barrels, so with the 1/16" twist, folks could reload cases with black powder, which did not work at all with the 1/12" twist of the .30/30! .30/30 cases had to be reloaded with smokeless powder. Otherwise, the .30/30 could only be fired two or thrtee times before crudding up so bad you couldn't hit anything with it!!
Some have said the reason was to use up .32/40 barrels that were rendered obsolete when Win. introduced the .30/30, but there is no proof of this. Even in 1895, Winchester (and others!!) could make barrels that were not accidentally oversize!!