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Thread: Powder Burn and Pressure Relationship

  1. #61
    Boolit Master uscra112's Avatar
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    Quote Originally Posted by 303Guy View Post
    Curious that they should light easier yet went out in the barrel when things were much hotter. Not enough oxygen under the conditions maybe? Mind you, enough oxygen will burn anything. Almost.
    In gunpowder, the oxygen is in the powder.
    So long, and thanks for all the fish.

  2. #62
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    Powder makes it's own oxygen so none is needed in the bore.
    Ever see the oxygen canisters in airplane ceilings? It uses a material that is ignited and gets hotter then blazes to generate oxygen.
    As to why kernels don't burn in the barrel is a mystery. Either they are driven ahead of pressure and out of flame or it is the dropping pressure. I have see too much left in brass though for that to be an answer. 3031 did that in the BFR 45-70. Yet the same load did well in a rifle. Is time a factor? What does primer pressure do?
    I would love to have a primer with a lot of fire and very little pressure to play with. Not the nature of the compound though with most primers having 2000 psi by themselves. The standard primer has almost as much pressure as a mag but I do see a difference with every single caliber change, larger needing the mag. I get the .454, .475 and even the JRH to light off with a standard LP primer but accuracy improves a lot with a mag. The opposite with the .44. If you say it is only cup thickness, I will say you are wrong, there is too much difference. Does the mag have a little more compound or is the formulation different?
    What affect does a primer have when you have unburned powder?
    I use a LP mag primer in the BPCR, 45-70 and put a disk of newspaper over the flash hole to keep powder out of the flash hole. The paper turns black but does not burn, some I pick out are still paper and you can read the print. I have never found the paper missing. The heat happens too fast and is gone fast. The primer just cuts a hole in the center.
    I also find Dacron on the range that has not melted. Wads under a boolit can be used again.
    To think there is a huge firestorm is wrong, the brass and barrel steel sucks the heat up.
    No math involved here from me!

  3. #63
    Boolit Master 303Guy's Avatar
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    In gunpowder, the oxygen is in the powder.
    Yes, but only so much. Enough for a stoichiometric burn or enough for a rich burn or enough for excess oxygen? Excess oxygen burns fuel faster and hotter. What I was thinking is that in air, there is all the oxygen in the world for complete combustion while inside the barrel there is only enough and that in the violent conditions in the bore the flame may go out when the pressure suddenly drops. By violent I mean things are moving around rapidly (plus all the other bits). One way of slowing a powder burn rate would be to provide less oxygen for a full burn i.e. a reducing flame. In a reducing flame there is a lot of CO produced and some CO2. All the H2 is burned regardless. In an excess oxygen flame all the CO is consumed to form CO2. In a stoichiometric flame most of the CO is consumed to form CO2. But in a barrel under flame induced pressure, the heat is required to release the oxygen so maybe at the point of pressure release, the temperature drops sufficiently to halt oxygen release and because of the motion of powder kernels combustion ceases. I'm not sure what fuels powder contains but I'm guessing it's not just carbon and hydrogen - that's what BP uses with some sulphur as a combustion accelerator. By the way, enough heat prevents CO from forming CO2 and actually causes CO2 to dissociate to form CO + O2 which then recombines as the temperature falls to release more heat.

    On the use of pistol powders in large cases, it makes sense for low velocity loads because those powders burn well and fast. The large case serves to absorb the gases produced, thus keeping pressure low but developing quickly and the larger the case the more gas can be contained which maintains the pressure longer as the boolit recedes down the bore.
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  4. #64
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    If memory serves me correct this subject has been discussed for years. Regardless of the continual discussions smokeless powders and BP have sufficient oxidizers in them. The small amount of oxygen that may be still in the case is of no measureable consequence. Hence in load development it is never a consideration.

    I am intrigued by your thesis of "But in a barrel under flame induced pressure, the heat is required to release the oxygen so maybe at the point of pressure release, the temperature drops sufficiently to halt oxygen release and because of the motion of powder kernels combustion ceases.". This may well explain why we get unburned kernels in cases of low expansion ration with some powders such as 3031/4895 in the 45/70(?) until a certain level of psi is reached.

    Larry Gibson

  5. #65
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    You bring up something of interest. Too much CO2 or other gases that damp flame.
    Now think a little. There is no free oxygen behind a boolit and no way for it to get in. There is a little in front of the powder charge but it is a sniff. From ignition to boolit release, there is NO additional oxygen except what powder produces. Even a grain of powder ignited makes oxygen. Nothing on earth burns without oxygen. The three things, fuel, oxygen and heat. Take away one and the fire goes out. Take away heat so powder can't make oxygen and you lost two for fire. Fuel alone does nothing by itself.
    Pressure is funny and you can cut steel with water pressure but it does not melt steel, it will not start a fire.
    When you pressure wash your deck, does it burn the wood?
    You turn gas into liquid with pressure and it is COLD, like propane or liquid nitrogen, CO2 is cold or made into dry ice.
    Compress air and the machine gets hot but the air is cold. Does pressure in a gun make powder burn? I would say the heat is like what a compressor makes at the piston that is doing work. Fill your compressor with high pressure air and feel the tank, will it start a fire?
    LOX is VERY cold.
    So does pressure in the gun actually remove heat? Is the high pressure what saves the gun from burning up?
    I am out of my element here. But an explanation of how pressure makes stuff burn faster unless you compress oxygen, release it to make stuff burn needs to be explained to my stupid brain. The fuel still needs heat even if sprayed with LOX.
    Oxygen will create heat through a nozzle when released and oil in an oxygen hose fitting will ignite. Out in the open, oxygen will not light oil without a heat source.
    The triangle can not be broken.

  6. #66
    Boolit Master 303Guy's Avatar
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    44man, you are by no means stupid. Heat and pressure are pretty much the same thing. Heat is the kinetic energy of molecules and pressure momentum energy - pressure is caused by molecules impacting on a boundary, in this case the chamber, bore and bullet base. The heat of compression in a comressor may not seem like much but remember that the pressure in a cartridge is a great deal higher, in the order of brazillion psi's. You will burn your hand on a compressore outlet at only 150 psi. A diesel engine will ignite its fuel just on the heat of compression. That's a cold engine (in the old days - my days - a heater coil was required to start a cold diesel engine).
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  7. #67
    Boolit Master madsenshooter's Avatar
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    303 guy, you mentioned IMR4007SSC previously. I just used the 43gr start load Hodgdon has for the .303 w/174gr j-word in a Krag with a 168gr cast bullet the other day. It burned well, pressure should have been relatively low, velocity 2300fps or so. The burn was fairly clean and accuracy wasn't too bad considering the velocity with a not too hard alloy. Others have said it burns dirty when you get down to cast pressures, but maybe they went down too far. It was cleaner burning than an equal charge of H414.
    "If people let the government decide what foods they eat and what medicines they take, their bodies will soon be in as sorry a state as are the souls of those who live under tyranny."

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  8. #68
    Boolit Master 303Guy's Avatar
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    Sounds good. It's available in my parts I see. Thanks, madsenshooter.
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  9. #69
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    Quote Originally Posted by 303Guy View Post
    44man, you are by no means stupid. Heat and pressure are pretty much the same thing. Heat is the kinetic energy of molecules and pressure momentum energy - pressure is caused by molecules impacting on a boundary, in this case the chamber, bore and bullet base. The heat of compression in a comressor may not seem like much but remember that the pressure in a cartridge is a great deal higher, in the order of brazillion psi's. You will burn your hand on a compressore outlet at only 150 psi. A diesel engine will ignite its fuel just on the heat of compression. That's a cold engine (in the old days - my days - a heater coil was required to start a cold diesel engine).
    For sure, compression does make a lot of heat and a compressor gets very hot like a diesel but once the air is out of the cylinder, it loses heat. If you spray fuel into the cylinder it will burn but you can not burn any if you spray it in the storage tank.
    So what happens to powder as the boolit moves and pressure is dropping?
    There might be something in what you say about grains bouncing all around and getting out of the flame. The fuel is no longer contained.
    Some powder can be ignited with impact like pounding out a stuck round from a chamber. That is like a piston.
    It gets harder---why will a powder not all burn in a short barrel so you have powder grains in the brass, bore and on the bench but it will all burn in a longer barrel? The pressure peak will be at about the same position and I can not figure what happens AFTER peak.
    Could time be a factor? Is time needed to erode the coating? Do grains of powder get slammed together hard enough to break the coating?
    I think about a catalytic converter where the platinum gets so hot it burns and alters all the gasses going through it. Why doesn't it melt the whole thing off the car?
    Is there a chemical reaction we miss?

  10. #70
    Boolit Master 303Guy's Avatar
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    I'm not aware of the platinum getting so hot. I suppose it does considering hot gasses are undergoing further combustion in contact with it.But it's the platinum causing the reaction, not just the heat. I think it is the time that makes a difference between a short barrel and a long barrel. The time required would be altered by raising the pressure and temperature with a heavier bullet or more powder.

    Just to clarify what pressure is; it's the total momentum of the gas and 'dust' impacting the container walls on a specific area, so a large number of molecules or dust particles at a lower momentum per molecule or particle would exert the same force as fewer particles or molecules with higher momentum. That's were temperature comes in. What temperature does is dictate the force of impact of the molecules against each other which is what causes chemical reactions - the high velocity impact of molecules which force say oxygen and carbon molecules or atoms close enough together to bond together forming CO2 (oxygen exists as O2).

    So I'm suggesting that as the projectile leaves the barrel the burning gasses rapidly vent out the muzzle, resulting in fewer high velocity impacts of molecules on burning kernels so they flame out. You see, although the molecules and kernels still have the same kinetic energy as before, they all move in the same direction and so don't impact each other any more. Well, not quite so simple as that.
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  11. #71
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    Too bad it can't be watched in ultra slow mo. Need a see through gun!

  12. #72
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    Just don't understand the quality of burn and pressure thing. Unless it's a chemical reaction rate that depends on pressure.

  13. #73
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    don't forget about the surface area of the powder.



    ohhh yeah, and I doubt anybody uses platinum in a cat any more, they use lot's of other stuff now like palladium.
    it's all an educated guess,,,, till the trigger is pulled.

    this opinion brought to you by mister low-tech solution..

  14. #74
    Boolit Master 303Guy's Avatar
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    Just don't understand the quality of burn and pressure thing. Unless it's a chemical reaction rate that depends on pressure.
    That's what I understand it to be, heat and pressure. But if one burns powder in air, I think something quite different happens. For a start there is plenty of time and the kernels stay together while they burn (and it's fun to watch). I've never tried a set up with some of the powder covered by something like sand.

    An analogy to try to understand heat and pressure and chemical reaction caused by it is to think of a shotgun loaded with steel shot. Actually, make that ball bearings. Anyway, if those are fired at a hard steel plate, there will be no collisions of the steel balls until they hit the steel plate and bounce back. Then a few will collide with a few of those still incoming. Now that plate will feel the effect of the multiple hits as pressure and it will act like the sides of a gas container for a few milliseconds.

    In a jet engine, two things are required to burn the air-fuel, firstly compression and secondly something to hold the flame retainer which also hold the fuel spray nozzles.

    Talking about unburned powder and those unburned kernels that light up easily, maybe this is what causes the mysterious SEE. Ignition occurs, the projectile moves forward down the bore dropping chamber pressure below that required to maintain a steady and progressive burn and the projectile slows (or maybe even stops) then the burn build up pressure and burns faster, too fast for the projectile speed to create more volume so the pressure runs away and we have a Ka-Boom! It all seems to make sense to me now.
    Last edited by 303Guy; 04-10-2013 at 03:33 AM.
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  15. #75
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    The powder burn rate is very much influenced by the pressure! With more pressure the faster it burns and with less pressure the slower it burns.

    The longer the length of time that the powder is subjected to a higher pressure the more completely it burns. This would be correctly called the “Time Pressure Curve”. An example would be a 30-30 Winchester and a 22-250, load them with the same powder and bullets of approximately the same sectional density, a 80 gr. 22 Cal. @ .228 and a 30 Cal. 150 gr. @ .226. The barrel volume in cubic inches for a 24” barrel in 22 cal. is 0.90 and a 30 cal. is 1.74, the 30 cal. has 0.84 more cubic inches of bore volume then the 22 cal. or 93% more volume.

    Because of the greater volume in the 30 caliber barrel, the “Time Pressure Curve” will drop at a much faster rate then the 22 caliber barrel directly affecting the combustion of the powder, leaving un-burnt powder in the barrel with a lower muzzle pressure at bullet exit.

  16. #76
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    The powder burn rate is very much influenced by the pressure! With more pressure the faster it burns and with less pressure the slower it burns.
    My SWAG on this is that the chemical reaction is different at different pressures, not the fuel/air ratio. Detroit reduced compression ratio to reduce NO byproducts. It fits with the low pressure ignition theory. My thought is the primer has to create the pressure (and heat of course) to create the proper reaction that burns fast. Some powder lights off and keeps the pressure up. Powder that doesn't 'light off' goes out the bbl or is left IN the bbl. as determined by bbl length and burn rate. This would also explain the position sensitivity and somewhat the S.E.E effect. My guess is Boyle's law and expansion ratio just determine velocity.

  17. #77
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    Understood pressure is needed.
    When I remove a fired case and pour out powder, just why didn't it burn when it is behind the peak and subject to all the pressure?
    There is just too close a relationship between pressure and fire. It would appear not enough fire does not aid the pressure work.
    How much pressure is needed? Looking at loads that run at 14,000 cup all the way to 60,000 psi, it is only the powder type and it's burning speed and how flame propagates.
    Gas can create huge heat when released fast as when it leaks past a boolit or out of a nozzle but most in he gun is kind of bottled up and the boolit base doesn't melt. You can get powder kernels impacting the boolit and making dents.
    You can make an airgun diesel with oil but I don't think powder will diesel.

  18. #78
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    Yeah, powder will diesel, Jim! Call it a SEE condition, if you and Larry will bend the rules a little. The ratio of air, heat, pressure is regulated for the powder designation. The "engineering" applications of shape, surface type, and porosity of the kernels is all in cahoots with the chemical deterrents to make up the "required" powder "speed" per cartridge. Ignition of the latter day smokeless powder design relies mostly upon the primer's wave production to overcome the various deterrent formulations. Also, additional air outside of the muzzle will make some powders act like a flame thrower. These powders are typically composed with heavy deterrents to maintain a low and LONG pressure curve intentionally for recoil reasons. These powders are typically triple based to keep pressure up to snuff throughout a long barrel (or a wide one). ... felix
    Last edited by felix; 04-10-2013 at 12:28 PM.
    felix

  19. #79
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    Triple based? Interesting, please tell us more. In fact anything on what makes up makes up a powder is interesting.

    Something about unburned powder I remembered from a discussion on muzzle blast suppressing firing tubes - the ones set up on ranges at the bench to shoot through. In particular, we were talking of a tube made up of car tyres. Apparently black powder can deposit enough unburned powder in the tube (or box) to ignite with a boom! I'm not sure if I can understand how BP doesn't burn completely outside of the barrel.

    Powder dieseling? That's a thought. Dieseling is ignition by heat of compression. The airgun dieseling is the perfect example of this. (It works best by squirting oil into the cylinder chamber and firing a shot before setting it up for the dieseling. That produces an oil 'smoke' in the bore just ripe for ignition. I have speculated that an oily chamber could cause dieseling behind the bullet by the pressure in the case injecting trapped oil into the throat. Whether there would be enough oxygen to burn it at that point, I don't know. There is air in the case and who know's whether more oxygen is released early to create an excess oxygen condition required but is so, it would unnaturally raise the pressure too early for the particular load. Plus it would be inconsistent from shot to shot so could upset accuracy that way. It may sound a little fanciful but I routinely lube my loaded rounds (not with oil - with case lube) and they come out the dryer after firing so there is a lot happening in there.

    I'm going to test the same powder and charge in my short barrel gun next. I know H4350 burned clean at quite low charges (60% load density) in its 15 inch barrel.

    don't forget about the surface area of the powder.
    H4350 looks identical to Varget the only difference being the kernel diameter. That would reduce the overall surface area (each kernel has a larger surface area).
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  20. #80
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    Nitro glycerin & nitro cellulose (TNT) are pressure sensitive and the primary components in smokeless powder. One could say dynamite doesn't need pressure, it actually creates it's own cause it 'burns' so fast. Kernel shape, surface area, retardants all control how much of the kernel can get burned at that instant, so yes they do control the 'burn rate'.
    NO is a wasted byproduct but NO2 releases oxygen to carbon when pressure gets high enough. Powder in the case is the same as powder in the bbl. Doesn't get consumed and gets left behind, although I've never seen it. I have seen left over in the bbl, from heavy loads.

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check