Men, I wrote to Sherman Bell to see if he had tested black powder cartridges to see what sort of pressures they generate. He mentioned that he had compared smokeless and Black powder pressures in two articles in the Winter 1999 and Summer 2002 issues of Double Gun Journal. He also mentioned that full power black powder loads produce from 6,000 to 8,000 psi breech pressure. By 'breech' pressure, I think he is referring to the hoop stress in the barrel near the breech (from how he uses that term in another article he wrote).
So that fits with the advice that has been given in this thread, but it is nice to have an idea where the upper limit is so one knows whether they have 7,000 plus or minus 5 psi to play with or 7,000 plus or minus 800 psi.
Not exactly, Kirk. Breech pressure is the peak/maximum pressure generated within the barrel and occurs before the payload (shot & wad) have moved into the barrel bore proper; this max pressure is within the chamber area and decays quickly as the payload starts to move. Hoop stress (the actual stress on the barrel steel) is calculated from knowing the barrel (chamber) ID, OD (hence, wall thickness), and breech pressure. Bigger diameters, thinner walls, and higher pressure cause higher hoop stress on the steel. The barrel profile is such that the hoop stress is never in excess of the yield strength (point where the steel bulges) of the steel. Per above, the pressure drops as payload moves down bore; so, the barrel walls may be made thinner. Questions?
DDA
