I got both my first deer and 1st elk with a Win 32 Sp back around '60. It was originally designed to duplicate 30-30 performance but could also be used with black powder. I don't know if this is true,...
I used to believe the same but I learned that was probably a myth. When you think about it, it doesn't make any sense as a bp round anyway, given the .32-40 and .38-55 that were bracketing it very closely and had the convenience of being straight walled cartridges.
http://www.chuckhawks.com/32spec.htm From Wikipedia. This duplicates what Speer wrote about it.
This cartridge is based on the .30-30 Winchester cartridge of 1895, but differs from the .30-30 in bullet diameter. More significantly, Winchester decreased the rate of rifling twist in their Model 94 rifle, from 1:12 when chambered for the .30-30 to 1:16 when chambered for the .32 Winchester Special. Winchester used the slower twist to reduce fouling retention when creating a
new cartridge for sportsmen who wanted to reload their own ammunition using black powder and cast bullets.[3] It was also marketed as something more powerful than the .30-30 and yet had less recoil than the .30 Army.[2][4] This new cartridge enjoyed only moderate success, and remained hampered by the small selection of available bullets in the .321 diameter.[2] There is a wide selection of bullet types and weights for the .30-30, while the only commonly available bullets in .321 diameter are 170 grain and 165 grain.
Also, due to the slow twist of the barrel, accuracy suffered when the barrel exhibited wear.