Re: Barrel making using draw-over-mandrel?

BP wrote in message news:100d0r8$12ddo$1@dont-email.me...
Jim Wilkins <muratlanne@gmail.com> 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
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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.