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Barlows Formula on a Contender bbl

Discussion in 'Shooting Related Threads' started by joe kuhn, Nov 2, 2009.

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  1. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    Found a discussion on another thread that shows the application of Barlow's formula on a gun barrel to compute bulge and burst pressures. Below is the entire quote and then I lay out the computation in detail.

    "What limits the use of high pressure cartridges in the Contender is the thickness of the barrel walls. The stress involved is referred to as "hoop stress" and is calculated with what is called Barlow's Formula.

    Pressure = 2 x Tensile Strength (PSI) x Wall Thickness (inches)/Outside Diameter (inches).

    For the pressure required to bulge a given barrel, use the Yield Strength of a material. For pressure required to rupture a given barrel, use the Ultimate Tensile Strength of a material.

    Using this formula, a Contender barrel diameter (.810"), and assuming a Yd Str of 110,000 PSI and a Ult Str of 135,000 PSI (the strengths for 416 stainless at a Rockwell C hardness of 26), a .308" bore would require about 68,000 PSI to bulge the barrel and about 84,000 PSI to rupture the barrel. The problem is the weak point of the Contender barrel is at the first forend bolt dovetail which removes .125" from the wall thickness. Pressures for bulge and burst then drop to 49,500 and 61,000. Going to larger bore barrels increases the problem."

    Computation details:

    Wall Thickness = .810 - .308 = .502/2 = .251

    Bulge pressure = 2 x 110,000 x .251 / .810 = 68,000

    Burst pressure = 2 x 135,000 x .251/ .810 = 84,000

    Joe
     
  2. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    Bulge pressure is the important one for me as I look for a doubles gun. I don't want to approach it. It's based on yield strength which is measured in psi.

    Yield strength is the pressure under which the form begins to yield or 'give way'.

    Notice the author lists hardness of the metal in his description: "416 stainless at a Rockwell C hardness of 26". Hardness is a basic property of metal. It's also listed in the above Website Address for 4140 steel as Brinell hardness. There are different measures for the property.

    I'm wondering if there's a derivative of Barlow's Formula, or a different formula entirely, for pipes that are closed on one end.

    Joe
     
  3. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    A good site discussing Barolow's Formula.
     
  4. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    Yield strength is nicely defined in WikiPedia.
     
  5. 221

    221 Banned User Banned TS Supporters

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    You should read what barlows formula is......

    <em>"Barlow's formula is merely a tool for burst estimation or prediction under ideal conditions at room temperature. Note that actual values may vary from these theoretical calculations for a number reasons"</em>

    It's even less accurate than Newtons laws are....for a number of reasons.

    All your fears are meaningless until you find the answer to what is going on with loads, both rifle and shotgun.

    As technology evolves tests are finding what we thought was accurate last week is not even close to reality.....As test resolution increases so does pressure and the number of spikes per shot.... IE....60,000psi ammo exceeding 80,000psi at a point in time that we know the bullet has left the barrel.

    You will lose your mind, if you keep chasing your tail.

    Maybe in your case a pair of H&R's with one of your famous stocks would be a solution to your phobia.
     
  6. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    221,

    I'm interested in the specific laws and the testing you refer to.

    I'm not interested in purchasing a K80 or a CG Summit because of their failures in the field. There are plenty of other guns to choose from. This isn't a phobia it's a choice. I'm exercising my right and freedom to choose as a consumer.

    Have you seen a proof sheet for the Blaser F3?
     
  7. rhymeswithorange

    rhymeswithorange Member

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    Blaser proof sheet probably looks a lot like Kreighoff's. Better stay away :>)
     
  8. joe kuhn

    joe kuhn Furry Lives Matter TS Supporters

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    Same bbl mfr or different?

    You guys must know something I don't. Perhaps it's a serial number range for the problems.
     
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