I'm thinking about making a reproduction medieval 'Handgonne' as per http://www.handgonne.com/ and http://www.musketeer.ch/blackpowder/handgonne.html. It will be .75" bore, and i'm trying to work out how thick the barrel needs to be. I can do all of the stress calculations no problems, but have no data on the pressures created by black powder. Does anybody have any sources of data/formulas to give an idea of pressures? I can then work out how thick the barrel needs to be in my chosen material, add a good safety margin and then crack on with manufacture. Obviously, I will be sending it for proof afterwards to make sure that everything is ok, but after all the work to make it, I want it to be ok first time.