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Can someone please explain why

Discussion in 'Handloading and Reloading' started by papajoe222, Sep 30, 2019.

  1. Jonesy814

    Jonesy814 Member

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    Tightgroup in 45 to Titegroup in 9mms is not a good comparison. Sure the bore is smaller in the 9 which results in less space for the gas to go, but the allowable pressure for 9mms is much higher
     
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  2. Walkalong

    Walkalong Moderator Staff Member

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    So true, but it happens faster in a high pressure small capacity case like the 9MM vs the low pressure large case .45 ACP, thus my comment as not being as user friendly, it can go from OK to bad quick, fast, and in a hurry in 9MM. At .45 ACP operating pressures if you go over a tenth or two you are still a good ways off from blowing up the case/gun. In the 9MM you are already up there pressure wise at max and when you go over that it's more hazardous, and with the case being so small it happens quicker as well.

    Reloading in general is dangerous if we are careless. Stay between the lines and stay safe. :)
     
  3. Walkalong

    Walkalong Moderator Staff Member

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    Yep, all because of the small case capacity operating at high pressure.
     
  4. Metal God

    Metal God Member

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    This isn’t about Titegroup, it’s the context in which the example was intended . Which is why you need to reduce your charge the heavier a bullet you use . If we start focusing on the powder and not the overall point we can easily loose sight on the original question.

    If you want to use Titegroup in a high pressure round pushing a heavy for cartridge bullet , be my guest . I strongly suggest you don’t try to get any high velocities with that combo .
     
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  5. thecarfarmer

    thecarfarmer Member

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    Why do you have to use more powder for a light bullet?

    Two words: nitrated fuel.

    Nitrogen bearing fuels as a class tend to generate more pressure if they meet with resistance.

    In other words, the more pressure they are under, the more they generate.

    The movement of the projectile down the barrel relieve this pressure, and a lighter, smaller bullet - or one that is not such a tight fit in the neck of the cartridge or going through the barrel - will allow the pressure to be relieved. In other words, the pressure won't spike as high.

    Incidentally, this is why nitrogen fertilizers can be mixed with a hydrocarbon oil, and will explode violently if contained under pressure, and why nitromethane makes so much more power than gasoline in an engine.

    Also, an engine running on nitromethane actually makes more power if loaded against a higher gear ratio. It allows the cylinder pressures to spike up higher, making more power, until... you get out the broom and sweep up car parts off the drag strip.

    Back to reloading, it's why a seemingly small change can push pressures over the edge.
     
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  6. Walkalong

    Walkalong Moderator Staff Member

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    Pressure and weight.

    Pressure, it builds faster behind a heavier bullet and we cannot get as much of the same powder in without going over the max pressure for the caliber.
     
  7. Walkalong

    Walkalong Moderator Staff Member

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    Agreed.
     
  8. Swampman

    Swampman Old Fart

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    Incorrect.

    The gas will build pressure until the bullet begins to move.

    If the gas keeps expanding and the bullet doesn't move, then the case and possibly the whole gun will fail.
     
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  9. Metal God

    Metal God Member

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    Swampman , it’s interesting you think I was incorrect. Please tell me how the gun or case will fail if the gases don’t continue to expand ? It’s that continuous expantion that causes the failure.
     
    Last edited: Oct 3, 2019
  10. hdwhit

    hdwhit Member

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    It doesn't.

    A lighter bullet can - at the extreme - be loaded on top of a heavier charge of powder, but there is no "requirement" to do so.

    If you are taking the charges shown in published load manuals as "required" then you are NOT following proper load development procedures. What you are doing may be very dangerous. STOP. Read the section at the front of your reloading manual (not just the load data at the back) as to how to begin with a Starting Load (it is called that for a reason) and then work your way up incrementally towards the Maximum Load (also called that for a reason) until you find the best combination of velocity and accuracy for your particular gun.
     
  11. Swampman

    Swampman Old Fart

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    There is no "specific rate" of gas expansion. By definition, the gas can't expand at all until there's space for it to expand into.

    Closed bomb testing

    As powder burns and creates gas in a firearm chamber, pressures rise and force the bullet to move, which creates space so that the gas can expand.
    Continuous expansion isn't as likely to cause a failure as building up pressure over a few milliseconds followed by a sudden, violent expansion.
    If the gas can't expand normally by pushing the bullet down the bore, then pressure will build up until something else gives.

    Then the gas may expand violently through the remains of your gun.
     
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  12. Metal God

    Metal God Member

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    (((There is no "specific rate" of gas expansion. By definition, the gas can't expand at all until there's space for it to expand into.)))

    Yes there is a space for it to expand into . The case , chamber and what ever amount of bore the bullet has moved to .

    I found nothing in the link that goes to what we are talking about here . In both examples the test allowed for full gas expansion as far as I could see .

    We are obviously getting past my pay grade but isn’t the burning powder creating gas . It sounds like you’re saying if the powder is burning in a closed system the gas does not expand . Meaning if you put 10gr of Titegroup into a sealed 55gal drum and ignited it , the gases would not expand , is that what you're saying because that goes against your link . If it does expand in a large closed system what makes it stop expanding in a small closed system like a plugged firearms bore ? If the gases are not expanding in a plugged bore , what is causing the pressure to rise ?

    If the powder is burning , the gases that is creating need to go somewhere ? Are the gases not continuously expanding into that fixed space regardless of size ? Isn’t that what creates the rise in pressure ?

    FWIW these are real questions not things I believe are facts possed as questions. I think of it as filling an air tank . Isn’t the air you are filling the tank with expanding into the tank resulting in builing up pressure with in that fixed space ?

    I mean how small are the molecules of gas from the burning powder . Don’t these gases start out very very small as the powder starts to burn . There should be plenty of space in the bore of a firearm for the gases to keep expanding until pressure is to great and things start to fail .
     
    Last edited: Oct 5, 2019
  13. LiveLife

    LiveLife Member

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    Compressing gas is not the same as powder "burning". Think of powder "burning" as solid matter "converting to gas state" and since gas state occupies larger volume of space than solid state, you either have expansion of space with no increase in pressure if not confined or increase in pressure if space is confined.

    It's like boiling a tablespoon of water into a large collapsed/flat plastic bag without increase in pressure vs boiling a tablespoon of water inside a 2 liter bottle. Unconfined, liquid water will change state to steam and inflate the plastic bag but confined by 2 liter bottle, liquid water will change state to steam and increase pressure, perhaps to point of rupture.

    I believe things happen much quicker and by the time the bullet is down the bore, maximum chamber pressure has already been reached and pressure is decreasing.

    Containing pressure of burning powder/conversion of solid granules to gas, is the job of the brass case. But I believe there is added factor of brass alloy's ability to stretch and how fast it can stretch (To seal case mouth/neck with the chamber to build pressure and shrink/retract case mouth/neck back so case can easily extract from the chamber - Wonderful quality of brass). New/newer brass may stretch readily (malleability) to contain the pressure whereas older/work hardened brass may not stretch fast enough and split/rupture causing case wall failure.
     
    Last edited: Oct 5, 2019
  14. Metal God

    Metal God Member

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    As you state above in both examples the water still creates steam . At what pressure does powder gases stop becoming gas and only create pressure ? There must be something expanding to create this pressure , right ? What is it if it's not the gas expanding . I'm ok with being wrong for calling it gas this whole time but there's got to be something creating the pressure if it isn't gas expansion ? or maybe expansion is the wrong word . Either way a big heavy slow bullet can't get out of the way fast enough and is why you need to reduce the charge .

    Why isn't compressing gas the same . The only difference is when filling the tank the gas is being supplied by an external supply while in a firearm it's being supplied by an internal supply . In both examples the more you put in the higher the pressure gets .
     
    Last edited: Oct 5, 2019
  15. Walkalong

    Walkalong Moderator Staff Member

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    The "Closed Bomb" test is where they get relative burn rates from, but it is not how powder burns in a rifle. Burn "rate", kernel size, coatings, case capacity, chamber size, bore size, bullet weight, friction, etc all affect how fast the powder burns. As pressure goes up it tends to burns faster and as pressure goes down it tends to burn slower. As space increases it tends to lose pressure.

    Lots of variable involved.
     
  16. Walkalong

    Walkalong Moderator Staff Member

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    Yep.

    Now, theoretically, the powder speed, case capacity, and barrel length could peak pressure right before exit I guess.

    But for the most part, pressure is diminishing when the bullet leaves the barrel.
     
  17. Metal God

    Metal God Member

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    I just need to know how the pressure goes up in a plugged bore if the gas is not expanding ?
     
  18. LiveLife

    LiveLife Member

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    Perhaps this will help.

    Below is pressure/time mapping of 180 gr bullet fired from 26" barrel .300 Weathrby Magnum where the bullet exits the barrel in 1.4 milliseconds. Maximum chamber pressure is reached in half millisecond with bullet having moved 2.8 inches. By the time the bullet is traveling halfway down the bore (almost a millisecond), pressure has decreased to 24,000 PSI and by the time the bullet is exiting the barrel, pressure has decreased to 100 PSI - https://gundigest.com/gear-ammo/reloading/bullet-ballistics

    Time (seconds) - Pressure (psi) - Velocity (fps) - Distance (inches)

    .0001 - 12,000 - 60 - .02
    .0003 - 36,000 - 500 - .60
    .0005 - 60,000 (near peak) - 1,400 - 2.80
    .0007 - 42,000 - 2,350 - 7.40
    .0009 - 24,000 - 2,970 13.80
    .0011 - 6,000 - 3,250 - 21.30
    .0013 - 100 - 3,300 - 26.00
     
  19. Metal God

    Metal God Member

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    Giving examples of the Firarms acting correctly it’s not helping this part of the discussion . The claim is if the bullet stops moving in the bore the gases stop expanding . I’d like to know why and or how that happens . Also what then creates the pressure that blows them up if the gas has stopped expanding .
     
  20. LiveLife

    LiveLife Member

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    I came late to your discussion after responding to OP just to clarify.

    I think your questions warrant a new thread discussion so as to not hijack this thread. ;)

    BTW, here's OP
     
  21. Swampman

    Swampman Old Fart

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    @Metal God

    From Google:

    ex·pan·sion
    /ikˈspanSHən/
    noun

    1. the action of becoming larger or more extensive.
     
  22. Metal God

    Metal God Member

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    So the gases are becoming more extensive causing pressure to rise ???? Which would mean expanding is the correct term ????
     
  23. Swampman

    Swampman Old Fart

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    My apologies sir, I now realize that the gas can expand as much as it wants to even though the actual volume occupied by the gas hasn't increased.

    Thank you for educating me and have a nice day. :notworthy:
     
  24. Nature Boy

    Nature Boy Member

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    I’ll add another variable on the pressure side of the equation and that’s bearing surface. Tangent ogive bullets have more bearing surface than secant ogive designs (SMKs vs VLDs). The former builds more pressure than the latter when charge weight and bullet weight are equal. At least that’s been my experience
     
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  25. Metal God

    Metal God Member

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    A gas is not a liquid it can be compressed therefore it does not need more space to create more volume . Just like filling a air tank . You can keep putting more and more in until if fails even though the volume of the tank stays fixed . You can continue to fill it with more and more air or gas , that air or gas just becomes more and more compressed raising pressure until it's released or failure of the tank .

    I keep hearing how I'm wrong but nobody has explained what is causing the pressure to rise in the bore if the gas is not expanding ? Something has to be happening to cause the pressure to rise . Just stating the pressure will keep rising is not an answer . We all know that or we would never see pressure signs or catastrophic failures .

    I've already said I may be wrong , I'd like a better understanding of how you're right .
     
    Last edited: Oct 5, 2019
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