I have reloaded black powder for the last 30+ years and it's quite safe.
Weight for weight it has @1/3'rd the energy of smokeless and the theoretical max. pressure of a bp burn lies in the 40kpsi range whereas smokeless will pass 200kpsi easy.
BP burns slow thats why they have such long barrels for rifle/shotgun cartridges.
http://www.ctmuzzleloaders.com/ctml_...p_burning.html
I think my bp load would put me in the 600fps range out of that 5" barrel.
It was for fun and giggles and i was a little suprised there was enough energy to rack the slide.