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Thread: Steel stress

  1. #21
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    I have seen results of real time pressure readings and peaks occur at various points in the bore as waves reflect from bullet to chamber and back.A peak can occur after the bullet has left the muzzle ,as a peak is reflected the length of the bore.These things are critical in large guns where size effects and weight considerations mean barrels my be working near their limit.

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    Another factor is surface area. The chamber area of a bottleneck cartridge has the largest surface area for the pressure to exert against. I would suspect the highest force in total exerted on a given section of barrel to be found in the front half of the chamber. With the heavier brass helping reduce the transfer of some pressure to the breech face and chamber walls at the very rear of the case.

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    Theoretically ,the sea should be flat(ish)...but it aint.

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    Quote Originally Posted by Monday View Post
    In which part of the chamber is the pressure/stress most high? Is it at the walls surrounding it or at the breech?
    Pressure at the breech is bolt thrust- the "equal and opposite" reaction to what's happening after primer ignition.
    Directly proportional to the case head diameter, it's the reason why heavier lugs/abutments at minimum are used on receivers suited for "boomers" like the .338 Lapua Magnum and .50 BMG. Chamber pressures are similar to other centerfire cartridges, but their large case head diameters create much more rearward (bolt) thrust.

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    Quote Originally Posted by 9100 View Post
    There is a limitation for the time a pulse takes to travel along a solid like steel. If you strike the end of a steel bar, there is a definite lag before it reaches the other end.

    How that relates to firearms is another thing. I suspect that the pulse would have to be extremely short or the chamber wall very thick for it to have much effect.

    Bill
    Barrel harmonics.
    And it has a significant effect- this "whip" of the barrel caused by the shock wave resonating from breech to muzzle, then back again- many times per second, is a large part of why every barrel shoots differently.

    Load development is geared largely toward finding the "sweet spot" of this shock wave to obtain optimal consistency/accuracy.

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    Quote Originally Posted by tobnpr View Post
    Barrel harmonics.
    And it has a significant effect- this "whip" of the barrel caused by the shock wave resonating from breech to muzzle, then back again- many times per second, is a large part of why every barrel shoots differently.

    Load development is geared largely toward finding the "sweet spot" of this shock wave to obtain optimal consistency/accuracy.
    The barrel mounting has a big part in this, no doubt much of the reason bedding makes so much difference and can be so critical. Doing accuracy tests, I clamped a .22 target barrel in a milling machine vise at the breech end. I could pluck the barrel like a tuning fork and the bullets were all over. When the barrel deflects, you don't want it to spring back. You want the bedding to be an energy absorbing material so it deforms with the first movement and does not send the energy back.

    At an NRA convention I happened to meet the VP of one of the better custom barrel makers, I don't recall the name right now. He told me that they would make 5 barrels for a bench rest shooter, one right after the other on the same setup. 4 would perform, the 5th wouldn't group.

    Bill


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