What is this? Vicksburg Tour --- "Vent Holes"

redbob

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Regtl. Staff Shiloh 2020
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Hoover, Alabama
According to the US Army's Artillery Museum's personnel, while firing locks had been used for some time by the US Navy, this was the Army's first efforts; the firing locks were manufactured by Enoch Hidden and used primarily on Bronze 6#ers (which was what we were looking at). While a number of guns were prepared for the locks, very few were actually used as they evidently were problematic and when asked what they looked like, the answer was: We don't know, if you find out please let us know. :cannon:
 
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ucvrelics

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Sounds like a challenge to me. Release The Hounds :D
 

redbob

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Regtl. Staff Shiloh 2020
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Location
Hoover, Alabama
And here is what started this conversation, these are field vent repairs and a blown vent. Photo by author.
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Noonanda

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Fredericksburg Virginia
I also have real concern when I see holes drilled in the breech "business" end of a cannon. If these 3 holes were drilled through to the bore, then that would really weaken the cannon. I would still be a little nervous having 3 extra holes bored through only half of the wall thickness of the breech.
As an engineer, I have to look at the stress analysis of this "modification". The cannon is classified as a Thick-walled Pressure Cylinder, meaning it is a pressurized cylinder that has a wall thickness that has a large ratio of Wall thickness to Cylinder Outer Diameter. The stresses that build up on a pressure vessel will be different for the different wall thicknesses.
I worked on aircraft Landing Gears and I didn't understand these struts(basically a hydraulic actuator) as a cylinder. It wasn't until I observed a test that used polarized light and a plastic coating that allowed you to actually see the stress patterns. Under pressure, the cylinder walls expands like a balloon. And these were steel cylinders that have a 1/4 inch, high-strength(Rc=52) wall.

I found this stress analysis of a thick walled cylinder that shows a Computer Model(FEM) of the stress patterns that would match what a cannon would be exposed to during firing.
Some of these stresses are for a closed cylinders---as the pressure expands, it causes the cylinder to grow longer. This would not apply to a Cannon that has an open breech. Also, the computer model looks at principal stresses which are stresses going in one direction.
FEA of Thick-walled Cylinder

Some images from that paper.
Notice in the Left image, the stresses are in the YELLOW range at almost half the wall thickness. If a hole is drilled into this stress zone, then this acts as a stress multiplier (aka stress concentration factor).
View attachment 332029

While your analysis is most likely correct (I am not an engineer so I have to take your word for it), I read somewhere that after the war the ordnance dept did a study and there was no records of a bronze gun blowing up during firing. There were (again IIRC) even records of in bore detonations by bronze guns that split part of the barrel but the gun did not break up killing the crew. While on the other hand Iron guns such as Parrotts had a nasty tendency to at some point in its life decide to "come apart". This as I understand was why the transition was made towards the Ordnance rifles
 
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