1/10 scale 1779 - 24 pounder build

Discussion in 'Cannon' started by Paul Buchel, Apr 27, 2014.

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  1. May 25, 2014 #41

    Zonie

    Zonie

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    I haven't used Cabot (Haynes?) 214 but Inconel 718 was my go to material for lots of structural applications in my gas turbine (jet) engines.

    Even Claypipe would like it!
    It's 184,000 ultimate tensile, 148,000 ultimate yield and 19.9% elongation aught to make one hell of a cannon barrel.

    Even at 1200*F it still has over 140 KSI tensile, 120 KSI yield and 18% elongation so shooting it in Phoenix, Arizona would be quite doable. :)

    Of course, there's the little matter of machining it. :(
     
  2. May 25, 2014 #42

    Musketeer

    Musketeer

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    1200*F is nothin'. That's considered a balmy day here in Phoenix. :wink: :blah:
     
  3. May 25, 2014 #43

    Guest

    So, in short, you are a troll, seeking to amuse yourself by playing that science guy?

    Oh, wait you had your fun, and now you are gone.
     
  4. May 25, 2014 #44

    davec2

    davec2

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    Clay,

    You may consider me a "troll" or whatever you like. And no, I am not gone...I just don't think you and I are getting anywhere on this particular topic. I have said what I needed to say on the subject of Velocity's cannon and so have you. Zonie and Old Ford and Musketeer VB have all expressed opinions as well. Now Velocity can decide what information he chooses to believe out of all that and how he wants to proceed based on all that information.

    I don't just comment on this subject, by the way. I have built more than a dozen cannon from 1 inch bore cast iron to 3 inch bore cast bronze and cast iron. I still own them all. I still shoot them all. And this will drive you really crazy...I built and shoot a 2.5 inch bore, steel lined, cast aluminum gun that works just fine with zinc balls and 1/2 pound charges. Recoil is a little heavy because the gun is so light, but the gun works just fine and shows no sign of distress after hundreds of rounds out of the tube. I just wanted to tell you that so that you understand that I am not just a theoretician...I do build and fire these things...with a linstock...so I'm standing right next to the damn things when they go off. I choose to believe my own calculations.

    Thanks again
     
  5. May 25, 2014 #45

    davec2

    davec2

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    OK....Claypipe accused me in a PM of wanting to have the last word....and then challenged me to post the calculations I sent to Velocity. Not sure those two comments go together, but here goes. The following is the important part of what I sent to Velocity originally. I can make this much more complicated if anyone wants to see it, but this is the straight forward, simplified version that I think presents a clear picture of the issue.


    "I did some quick hoop stress calculations...the yield strength of your material is about 170 MPa (24,600 psi). The Ultimate strength is 360 MPa (~ 52,200 psi). The stress in the wall is equal to the pressure x the mean diameter divided by twice the wall thickness. In your case (assuming the breech area is 1.5 inches in diameter and the bore is .5 inches) and that the charge can generate 10,000 psi bore pressure (very high estimate for 40 grains of black powder), the calculated stress in the wall is 7,500 psi. This is less than one third the yield strength of the PB1 material. Even if we assume the bore pressure is an unreasonable 20,000 psi, the stress in the wall is only 15,000 psi, just two thirds of the yield strength. No yield, no "elongation" and no "fatigue". Your cannon is perfectly safe as is."
     
  6. May 25, 2014 #46

    Guest

    Hey, what do I know, I'm just a dumb gunner.

    Well, you are in the running for the Darwin Award. When's the last time you had that thing x-rayed or Magna-Flux?

    The one thing that many a civilian cannon disaster has had in common? They all knew what they were doing. Just like the mythbusters.

    Oh, you wanted an example of a machine shop project gone bad. See if this fits the bill. Admittedly Human Arrogance was a major contributing factor.
    http://www.seattlepi.com/local/article/Boy-hurt-by-cannon-blast-feels-twice-wounded-1222900.php
     
    Last edited by a moderator: Oct 27, 2018
  7. May 25, 2014 #47

    Guest

    Since, admittedly you know more about the math of stress.

    What would be the equation for the pressures generated when the bore becomes sealed at mid to three quarter point?

    Due to, say, a lead or zinc ball having an internal void. Which causes the ball to expand, plugging the tube.

    Or a gust of wind blowing sand and/or debris down the bore.

    Or a small child putting something in the bore. A pebble, twig, gum, etc.

    Or a forgotten rammer. Yes, this has happened.

    These are common hazards one has to be alert to, when working with artillery, whatever the size. And all effect the pressures the tube is subjected to.

    As careful as one maybe, stuff happens.
     
  8. May 25, 2014 #48

    Paul Buchel

    Paul Buchel

    Paul Buchel

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    So, you admit that Davec2 is correct?

    Your post is off topic, as we were discussing the use of PB1 bronze in my cannon.

    My .44 cal lead balls are made by Frontier metal processing, I have 200, they all weigh 127gr

    My wife and I have never had children. All firearms should be kept out of the reach of children anyway!!!

    The ramming tools I have not even considered yet.
    leaving a ramming rod in the barrel must have been one of the children.

    Dust, sand, no, we have lovely grass.

    I live in a nature reserve, with thousands of different insects. Wasps and Hornets would love this barrel, that is why I have already made a plug. BTW, I had to abort takeoff in my aircraft as a wasp had made it's nest in the pitot tube.

    Regards Paul.
     
  9. May 25, 2014 #49

    Rifleman1776

    Rifleman1776

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    "breath"??? :confused:
    "give"??? :confused:

    Staying polite.....spiking that beautiful cannon borderlines on sin. :(
    It should be used and enjoyed.
     
  10. May 25, 2014 #50

    davec2

    davec2

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    Claypipe,

    Wow!!! And what if a meteor hits you while your firing your cannon???? Then what ???? Or if a commercial airplane crashes into you???? So much to worry about when using cannon !!!!
     
  11. May 25, 2014 #51

    davec2

    davec2

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    Claypipe,

    Sorry for the last response.....I was just being a wise guy. I don't think your a "dumb gunner" , by the way. (In the Navy they used to call those of us in gunnery "cannon cockers".) I understand that there are a lot of things to be careful about when dealing with firearms, especially cannon. I just don't want you to worry about things that really don't need to be worried about. It takes so much of the enjoyment out of something that should be great fun !! Safe fun, but great fun.

    I read the article you sent me the link to. I did not see anything specific about what happened. Is there any more information about the gun or what caused the accident??

    Thanks

    Dave c
     
  12. May 25, 2014 #52

    Guest

    All of the scenarios that I have listed are far more possible to occur than what you counter with.

    Having done public demos, I have personally encountered many of these perils. That's why guards are posted and tampions are put in place.

    So, Using a PB1 tube, 50 grains FFFg and a defective lead ball, what would you calculate the pressure to be, with a .50 tube 12 inches in length, with an OD of 1.50" at breech and OD of 1.0" at the muzzle, with an 11" Bore Length and bore blockage at 2" from the muzzle?
     
  13. May 25, 2014 #53

    Guest

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  14. May 26, 2014 #54

    Zonie

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    A defective ball with a void as you suggested would shoot just like a solid ball providing it is rammed against the powder load.

    It will not expand or plug the bore if it is properly loaded.

    As the breech pressure is directly related to the weight of the projectile, the breech pressure would be less with the defective ball because the weight of the projectile would be less.

    As for firing any gun with a bore that is obstructed by something like a second ball partially rammed, snow, mud etc. even a barrel made from a high strength heat treated steel will probably explode.

    I'm sure davec2 was speaking of a properly loaded barrel with a correct charge when he said the cannon was safe to fire.
     
  15. May 26, 2014 #55

    davec2

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    Claypipe,
    As Zonie notes, a defective ball cannot plug a bore by expanding due to a void or even by obduration under acceleration. Minne bullets are made to expand into rifling and do not appreciably increase pressure. And he is also correct in that a lighter ball equates to lower breech pressures. In the case of some complete and un-noticed bore obstruction, there is a chance of rupture. And that would be true for PB1 or SAE660 or any one of a number of materials. However, it would take a pressure in the barrel in excess of 69,600 psi to fail the PB1 material (i.e. exceed its ultimate strength of 52,200 psi. It would start to yield at 32,800 psi.) Nonetheless, even with 50 grains of black powder, I am not sure you can generate 69,200 psi in a .5o cal tube 11 inches long. That is a different set of calculations. I can do it for you, but I need some reference materials I do not have with me as I am traveling on the East coast on business until mid June.
    As Zonie said in his post, when I say the PB1 barrel is safe to fire, I mean properly loaded and with no bore obstruction. Just like any modern firearm, it would be perfectly safe unless it is severely abused by overload, or fired with a bore obstruction. If the point here is to make a barrel completely disaster proof in the face of any kind of overload, bore obstruction, or abuse, you can bet that SAE660 would not fare any better than PB1. However, I can make a barrel out of INCO 718, put a breech plug in both ends, put 50 grains of BP in it and fire it with no ill effects at all. I routinely make rocket parts that would easily take that kind of pressure without failing or yielding”¦but I don’t think you want to insist that all future cannon be made out of 718. Besides, what I am saying here would only apply to a .50 cal barrel with a 1.5 inch breech diameter.
     
  16. May 26, 2014 #56

    Zonie

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    Ummmmmm...

    Before someone starts thinking the tensile or yield strength of a material is the same thing as the pressure inside a gun barrel that it will safely take, they need to know a little about how these material properties work.

    A material that has a ultimate tensile strength of say 40,000 PSI might contain, or might not contain that much bore pressure. In many cases it won't.

    The value represents the amount of force needed to break a part with a crossectional area of 1 square inch. That is, if you had a 1 inch X 1 inch bar 12 inches long, it has a crossectional area of 1 square inch.

    If the crossectional area is only 1/2 square inch somewhere in its length then it takes only one half of the tensile force (load) to break it.

    For instance, because a barrel is hollow, the actual amount of material in the wall of the barrel at any linear distance along its length may be far less than 1 square inch.
    It is the value of that area that must contain the barrels pressure.

    Just for giggles, let's say you have a barrel that is 3/4 of an inch in diameter and it has a 5/8 inch bore in it.
    When you figure the area of the outside and subtract the area of the inside the crossectional area of the tube is equal to 0.135 square inches.
    That's only a little over 1/8th of a square inch.

    If the material had a ultimate tensile strength of 40,000 psi and you applied a weigh of 5400 pounds to it so the weight was using the tube to keep it from falling the weight would rip the tube apart.

    Then, figuring hoop and barrel stress gets even more complicated and it would make many people get a headache if I explained it so I won't.

    Then, even when figuring hoop stress in a round container or barrel, there are different safety factors that need to be considered.

    If a nice gentle pressure build up is what the container will need to withstand then a safety factor of 2 might be in order.
    My books dealing with this sort of situation say if the force is a "explosive" force, the safety factor in determining a safe wall thickness should be 4. In other words, it needs to be 4 times stronger than the calculation would at first indicate.

    The bottom line is, even if the barrel is made out of a material with a large value for its "ultimate tensile strength", it may fail even though the breech pressures in the barrel are far lower than that tensile value.
    If the barrel wall is too thin even a breech pressure of 4,000 psi could cause a material with a tensile strength of 80,000 psi to fail.
     
  17. May 26, 2014 #57

    Paul Buchel

    Paul Buchel

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  18. May 26, 2014 #58

    davec2

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    Zonie,

    You are absolutely correct. The numbers I ran for Claypipe are hoop stress and represent the pressure required in the bore to generate a stress in the wall equal to the published ultimate and yield data. For things that stay on the ground, we often use a safety factor of 4 to come up with an acceptable working load. For things that have to fly, the safety factor is often between 1.25 and 2. And, you are right, that a "rapid" application of force is different than a gradual increase. I was just giving Claypipe a feel for how much pressure we are roughly talking about to yield or break something with a 1/2 wall thickness and a 1/2 inch ID.

    By the by, if you look at Velocity's other pictures you can see a pair of cannon barrel box lock pistols. I would bet that they are originals with cast brass barrels with all the metallurgical purity an 18th century founder could muster. Probably near .44 cal and probably using 20 to 30 grains of BP to fire a round ball. And I bet the breech is not a 1/2 inch thick and that they safely passed proof early in their lives and have survived ??? firings to the present. Just noting this as a point of reference since the pictures are right next to Velocity's new cannon.
     
  19. May 26, 2014 #59

    F.G. Ford

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    Hi Paul,
    Awesome work!
    Thank you for posting.
    Best regards
    Fred
     
  20. May 26, 2014 #60

    Rifleman1776

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    :shocked2: We are way past that possibility. :rotf:
     

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