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Thread: Dented ammo question

  1. #21
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    Quote Originally Posted by Bret View Post
    I've done that myself, but he's talking about the neck.
    Yea. My Mini-14 dents the neck when a loaded magazine (even partially loaded) is inserted with a closed bolt.

    Buddy said the dented case was dangerous. I disagreed.

    I do not reload rifle ammo and don't plan to.

  2. #22
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    Spent case necks getting dented from the ejection process is pretty common. If it's not too bad, the dent is removed in the sizing step. If it's kind of bad, then the neck might have to be straightened a bit before sizing. If it's mangled, then most just toss the case. The thing that confuses me about the OP's question is that he talks about the case neck firing forming in the chamber. That would make sense for the body or shoulder, but not a neck. It should always be in a cylindrical shape after sizing.
    Last edited by Bret; 08-31-21 at 13:29.

  3. #23
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    Quote Originally Posted by markm View Post
    It can happen if a guy overdoes it on case lube. It hydraulics a dent in the shoulder usually.
    I've done this with 30-06 and 8MM. ^^^^^^^If the dent does not significantly deform the case, I fire the round and the dent comes out on it's own.

    I've also seen freshly opened boxes of bulk M193 that had dented cases.
    Train 2 Win

  4. #24
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    Quote Originally Posted by SomeOtherGuy View Post
    I'll try, but maybe an engineer or industry type can do better.

    All propellants have an inherent burn rate. Most have an increasing burn rate as temperature and pressure increase. Inside a case there is total confinement on all sides except the bullet, which provides limited confinement due to its mass and resulting inertia. The bullet also has a slight "stiction" to overcome before it starts moving - that depends on crimping, and if you jam a bullet into the lands (which would be a longer OAL than normal) it gets worse.

    Primer ignites, propellant all ignites as a result. The propellant creates a certain volume of gas based on its quantity, burn rate, and how good the primer's ignition was. This initial volume of gas starts moving the bullet, and also accelerates the burn rate of remaining propellant. But the bullet doesn't move instantly, and its initial movement is, relatively speaking, slow.

    Let's say you have 8 grains of propellant in a .40 S&W case, bullet properly seated. It reaches 35k psi, which is OK. Let's say you seat the bullet too deep and there's only 90% of the intended volume. Pressure reaches 110% or 38.5k psi, which is over pressure but probably won't break anything. Except propellant burn rate increases with pressure, so in fact having 90% of intended volume might create 120% of intended pressure. That's near a proof load. Go to 80% volume, maybe you get 140% intended pressure, things start breaking.

    Not an expert but that's my understanding.
    It's called starting pressure and it is critical.

  5. #25
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    Quote Originally Posted by SomeOtherGuy View Post
    I'll try, but maybe an engineer or industry type can do better.

    All propellants have an inherent burn rate. Most have an increasing burn rate as temperature and pressure increase. Inside a case there is total confinement on all sides except the bullet, which provides limited confinement due to its mass and resulting inertia. The bullet also has a slight "stiction" to overcome before it starts moving - that depends on crimping, and if you jam a bullet into the lands (which would be a longer OAL than normal) it gets worse.

    Primer ignites, propellant all ignites as a result. The propellant creates a certain volume of gas based on its quantity, burn rate, and how good the primer's ignition was. This initial volume of gas starts moving the bullet, and also accelerates the burn rate of remaining propellant. But the bullet doesn't move instantly, and its initial movement is, relatively speaking, slow.

    Let's say you have 8 grains of propellant in a .40 S&W case, bullet properly seated. It reaches 35k psi, which is OK. Let's say you seat the bullet too deep and there's only 90% of the intended volume. Pressure reaches 110% or 38.5k psi, which is over pressure but probably won't break anything. Except propellant burn rate increases with pressure, so in fact having 90% of intended volume might create 120% of intended pressure. That's near a proof load. Go to 80% volume, maybe you get 140% intended pressure, things start breaking.

    Not an expert but that's my understanding.
    Can you link to me somewhere that explains how burn rate has a significant increase as pressure rises? That seems backwards. I’ve been under the impression that burn rate remains relatively stable, but temperature has a direct relationship with burn rate, thus increasing pressure all things being equal.

    The way you’re explaining it, it would be an exponential relationship as higher burn rate equals higher pressure which equals higher burn rate.


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  6. #26
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    Quote Originally Posted by mRad View Post
    Can you link to me somewhere that explains how burn rate has a significant increase as pressure rises?
    I can't find anything authoritative offhand. I found this forum post (yeah, who knows) saying the same thing:

    https://www.bullseyeforum.net/t2279-...uivalent-chart

    The problem with burn rate charts is that they are speculative, or in other words, educated guesses. None of these charts are arrived at by testing each powder in the same application to determine how they line up in terms of burn rate. A characteristic of smokeless powder is that as the pressure goes up, the burn rate increases disproportionately faster. This is why you can get to a point where the pressures spike with small charge wt increases. The chemical makeup of a powder can determine how fast the burn speed increases as the pressure goes up. Some powders increase faster or slower than others. This simply means that you can make some general assumptions by looking at burn rate charts. However, just because a powder is located at the same level as another on the chart does not mean that these two powders are indeed the same, nor does it indicate these powders will react the same in different pressure ranges.

    Quote Originally Posted by mRad View Post
    That seems backwards. I’ve been under the impression that burn rate remains relatively stable, but temperature has a direct relationship with burn rate, thus increasing pressure all things being equal.
    The way you’re explaining it, it would be an exponential relationship as higher burn rate equals higher pressure which equals higher burn rate.
    Under the ideal gas law, in a confined space more temperature creates more pressure, and more pressure creates higher temperatures. So while I can't find another direct statement that the burn rates accelerate with pressure, it seems to follow from basic gas physics. There are various statements that double-base propellants (containing nitroglycerin) burn faster at higher temperatures.

    https://infogalactic.com/info/Ideal_gas_law

  7. #27
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    Quote Originally Posted by mRad View Post
    The way you’re explaining it, it would be an exponential relationship as higher burn rate equals higher pressure which equals higher burn rate.
    I believe it is. Search for Vieille's Law.

    https://www.nakka-rocketry.net/burnrate.html

    https://bisonballistics.com/QuickLOAD.pdf (page 97)

    http://www.wydawnictwa.ipo.waw.pl/ce.../Boulkadid.pdf
    Last edited by Disciple; 09-03-21 at 13:15.

  8. #28
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    Reading through, how would Saint Robert’s law apply? And the N value would determine to what degree burn rate increases, am I understanding that right? And the closer to zero the N value is, the effect would be less.

    Where I’m struggling to apply it to gun powders used on most modern cartridges, velocity would likely decrease as charge and pressure increase on larger cartridges.

    Perhaps pressure never gets high enough for the phenomenon to exist on rounds we commonly shoot. I don’t know, more or less thinking out loud. It’s an interesting subject.


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  9. #29
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    Quote Originally Posted by T2C View Post

    I've also seen freshly opened boxes of bulk M193 that had dented cases.
    Common from what I've seen.

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