Wall thickness, pressure and steel

Discussion in 'Blackpowder' started by Revolver.45, Jan 29, 2020.

  1. Revolver.45

    Revolver.45 Member

    Jan 29, 2020

    I’ve seen old black powder revolvers with very thin cylinder wall thickness, like these cylinders for example:


    and this pepperbox has also resonable thin walls:

    Back in the days the quality of steel was inferior, so it got me to wounder about the steels of today.

    What’s the minimum (with a safety factor) thickness of a chamber (or overall barrel for a pepperbox or derringer) in cal .40 containing a 25-30 grain FFFG black powder (or equivalent pyrodex P) load with a 92 grain lead roundball tightly infront of it (+wadding) if it’s made out of a steel with following properties:

    Yield strength min [MPa]

    Tensile strength [MPa]

    Elongation A5 [%]

    270-325 HB

    And how many PSI will such a load described above generate?
  2. ofitg

    ofitg Member

    May 17, 2010
    The old 1975 Lyman Black Powder Handbook lists the following data for a patched 92-grain lead ball - 2690 LUP (Lead Units of Pressure) with 25 grains of Gearhart-Owen FFFg, and 3760 LUP with 30 grains of G-O FFFg.
    LUP is not equal to PSI, but it should be in the ballpark.

    I would note that the 1975 G-O powder was produced at the Moosic, PA plant, which was shut down twenty-some years ago. The 1975 G-O powder was apparently comparable to the Swiss or Old Eynsford powders which are available nowadays.
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