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Arguing about pressure?

Discussion in 'Shooting Related Threads' started by 9point3, Apr 5, 2011.

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  1. 9point3

    9point3 Well-Known Member

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    Have any of you guys that are discussing safe and prudent pressures ever take into account bore diameter and its relationship to pressure?
     
  2. leadvail

    leadvail Member

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    I"ll bite...Not yet. Why?
     
  3. 9point3

    9point3 Well-Known Member

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    Seems to me that pressure with a given load will be lower when shot through a larger bore

    I'm not really concerned about it as I load from the low end of the chart but the way others were arguing their points regarding Red Dot and safe pressures a I was suprized bore diameter was never mentioned
     
  4. leadvail

    leadvail Member

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    Youre right. Somebody did mention 28 ga having over 12500 psi. I think 20, 28 and 410 are higher also.

    Need an expert to look it up and explain it further, do they use better barrel steel or.. it's a conspiracy against trapshooters.


    I have only used loading data recommended in the manuals by the professionals and never paid any attention to the pressure readings when I load for my smaller frame SP Beretta's.
     
  5. 9point3

    9point3 Well-Known Member

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    I was thinkin more along the lines of a standard .729 bore vs a back bored barrel, be it factory or aftermarket
     
  6. leadvail

    leadvail Member

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    i am sure someone here will know. good luck
     
  7. ivanhoe

    ivanhoe Well-Known Member

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    If that were the case(lower pressure in larger bore dia.)why are they not stated as such in reloading manuals?

    It would seem if it increases or decreases pressure shouldn't it given in the manuals to keep the reloaders informed?

    Bob Lawless
     
  8. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    The 12 ga. chambers are all standard size regardless of bore size. That's where the pressures are measured.

    Hap
     
  9. 9point3

    9point3 Well-Known Member

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    Hap,

    Pressure is measured at the chamber but an increase in bore diameter makes the pressure vessel larger therefore increasing area and lowering PSI

    Sarge,

    Measuring pressure in a standard SAAMI chamber and barrel is fine for a base line but each firarm is a bit different in demension and pressurs will be different, just ask a rifle re-loader a load that shows pressure in my rifle might not in yours
     
  10. Unknown1

    Unknown1 Well-Known Member

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    ...and somebody wanted to know if trap shooters over-analyze things?

    MK
     
  11. timb99

    timb99 Well-Known Member

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    Not only that 9point3, for any given pressure, a smaller diameter tube will result in a lower force acting on the tube walls.

    Pressure times area equals force, and a smaller barrel has smaller area for the pressure to act upon.
     
  12. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    It's great to learn something new, thanks for the information!

    All my time reloading both rifle and shotshells I was under the impression that "chamber" pressures were measured about the time the wad or bullets completely exited the confines of the shell or casing!

    Are all chamber pressure guns made to the same specifications for measuring? That, whether it's LPUs,CPUs or PSI? The pictures I've seen have the pressure rods located near where the base wads and powders meet in the shell if memory doesn't fail me?

    Roy Weatherby found he had to increase the throat length in his mag cal rifles to prevent building excess chamber pressures. Those mags have much more freebore than standard rifle calibers have before the bullets touch the rifling. We used to place a white sheet on the ground in front of a couple Weatherbys to see if all the powder sticks were consumed. Sometimes the powder grains we'd pick off that sheet were 3 to 5 grains of powder, weighed.

    One more question, if the pressure guns are all standard chambers and cylinder bored for measuring shotshells, how do we know what the chamber pressures might be with various bore sizes? With shotshells only.

    Hap
     
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