The little nub doesn't direct gasses away from the gap.
The man who makes wood boxes shaped like people has hit the nail on the flat part!
I've wanted to try a Model #3 Schofield S&W for a number of years but had always heard the Italian import Schofields, chambered for the 45 Colt rather than the more correct 45 S&W, did not play well with black powder. Believing S&W's propaganda about the 2000 Model Schofield being an "exact reproduction" I eventually bought one those more expensive recreations.
Just as Coffinmaker said, S&W's little nub which replaced the actual bushing the original's had, didn't play well with BP either. My copy was so bad, even with Big Lube bullets it would not fire more than 4 rounds, and the cylinder had to be turned by hand to get the 4th chamber in alignment. It wouldn't budge for the 5th round.
The solution (other than selling it) was to use my last can of Black MZ substitute which got me through 25 rounds without cleaning. I'm told the Black MZ is nothing more than APP so if the Schofield is still around when this stuff runs out I will seek out a can of American Pioneer Powder.
Bottom line is a properly, traditionally designed cylinder bushing is almost a necessity for shooting black powder.
Dave