Go over to sassnet.com and ask this question on their "Wire" forum...
There are plenty of Cowboy Action Shooters that shoot this round in Long Range Side matches.
BTW, (out of a good barrel) the .32-40 is an incredibly accurate round, even (especially?!!) shooting Lead bullets.
In fact if was one of Harry Pope's favorite accuracy cartridges (I believe some of Pope's shooting records, using Blackpowder, remain unbeaten

).