From: muratlanne@gmail.com   
      
   BP wrote in message news:100d0r8$12ddo$1@dont-email.me...   
      
   Jim Wilkins  wrote:   
   >   
   > Around the time of the US Civil War military barrels were rolled out from   
   > short thick blanks over a mandrel, then drilled to size, rifled and   
   > straightened by expert hands.   
      
   At least superficially the DOM process could combine drilling, rifling   
   and straightening steps into one, or at worst two, using nearly identical   
   machinery. What am I missing? Is the problem a too-small final ID?   
      
   It does occur to me that the pull strength of the internal mandrel grows   
   as the square of the diameter, while the pull force likely grows linearly   
   with the circumference. I suppose that would set a lower bore limit....   
      
   Thanks for writing,   
      
   bob prohaska   
      
   -------------------------------------   
   What you are missing may be proprietary trade secrets concerning the   
   relative strengths and weaknesses of hammer forging, button rifling and   
   drawing over a mandrel, all of which are similar. I suspect the fittest   
   survived.   
      
   The answer may depend on plastic deformation and work-hardening of a thick   
   walled pressure vessel, which is one with varying stress and strain   
   distribution across the wall thickness. Before tech permitted big gun   
   barrels to be forged in one piece they were built up from concentric   
   cylinders successively heated to expand them and shrunk together, preloading   
   the inner layers with compressive force. Expanding the barrel over a mandrel   
   might have the opposite effect, or see below.   
      
   https://en.wikipedia.org/wiki/Built-up_gun   
   "Theoretical maximum performance would be achieved if the inner cylinder   
   forming the rifled bore were compressed to its elastic limit by surrounding   
   elements while at rest before firing, and expanded to its elastic limit by   
   internal gas pressure during firing."   
      
   This is more or less what you suggest:   
   https://en.wikipedia.org/wiki/Autofrettage   
   "In modern practice, a slightly oversized die is pushed slowly through the   
   barrel by a hydraulically driven ram."   
   I didn't learn nearly enough in one semester of Materials Science to   
   understand the subtleties of plastic deformation beyond the yield point.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)