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Discussion Starter · #1 ·
This might be one for Myth Busters.
I've been all over the net - no clue.
Lot's of burn rate charts, and a few pressure vs travel curves.
But no answer regarding how long the combustion phases lasts.

We are all familiar with the pressures involved.
I've found temperature estimates - 2000 - 4000 F?

Given - it burns faster under pressure.

5 seconds or so it takes to burn 10 grains in free air.
But in a cartridge, in a chamber???

Order of magnitude? Pistol or rifle?
Milliseconds?
Microseconds?

I know it's not fast enough to generate internal shock waves (eg: explode)

When it is first ignited in an enclosed cartridge case, it burns slowly there too,
for the first imperceptible fraction of a second. That initial, slow burn releases
a bit of gas though, and it quickly pressurizes the inside of the case.
As the pressure ramps up, the powder burns even faster, causing even more
pressure.
Of course, all of this happens in an instant as far as we can tell, but if you could
watch it in ultra slow motion, that’s what you would see.
So the question is:
How long (time or distance) does powder burn?
Time - as in milliseconds?
Or
Distance - as in inches down the barrel?

Smokeless powder contains its' own oxygen.
But how long does that last?

I don't think we can say all the way to the end of the barrel.
We've all seem those magnificent fireballs from the big bore magnums.
Smoke will burn and my intuition says that those fireballs are hot gasses
meeting free O2 outside the barrel - and the powder itself is already long gone.

Probably at the peak of the pressure curve?
After that point the pressure is dropping (duh!) and the burn should be slowing down?
Or go out completely?
That would probably indicate 2 or 3 inches down the barrel at most.

from Chuck Hawks site:
Relative quickness is defined by "closed bomb tests," which quantify pressure rise in a sealed container. However, professional ballisticians do not use relative quickness for load development, either. A closed bomb relative quickness value does not translate into any type of value outside of that 'closed bomb' test. Powder performance varies widely by actual application. Relative quickness is one of several preliminary considerations when assessing a powder's suitability for a particular application by ballistics, but nothing more than that.
 

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I don't have any exact answers, but we cam look at some of the parameters it's working under.

Assuming a 45 firing a 230gr bullet with a muzzle velocity of 800 fps, we can compute the time in the barrel, That works out to 0.0009375 seconds in a 5" barrel. This assumes the base of the bullet is 0.5" ahead of the breech, giving bullet travel as 4.5".

Whether or not the powder has completely burned, that's how much time it has in the barrel to push the bullet.
 

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This is a pretty interesting question. And I have made some casual observations on this subject over the years. One of the observations that I have made is that to really get a handle on this you would need to have some pretty high end measuring equipment at your disposal. Proceeding from there. You can go on to extrapolate information provided by other sources that would presumably be presenting information that they have derived from sources with advanced instrumentation designed with measuring this in mind.

My experience as a hand loader has led me to believe that this is in fact the case. The powder manufacturers are producing some pretty good products these days. But they have not resolved many of the issues by any stretch of the imagination. Point in fact is something that I am a bit acquainted with. Pistol caliber carbines. Studies produced of late will clearly indicate for instance that generally speaking pistol caliber carbines chambered in 9X19 will gain a significant velocity increase over the same round being fired out of a typical handgun length barrel. While on the other hand, the .45 acp round will not. Hmm.
A further observation on this as made by someone other than myself has this to say. Regarding the .45 Colt round out of a carbine/rifle. That you do not gain any significant velocity increase out of a rifle length barrel for this round because the powders suitable for loading the round will not gain anything from this. OK I can kind of buy this making the assumption that these people actually know what they are talking about. Additionally certain assumptions need to consider whether or not faster is always better. But that is a whole other subject.
More recently a lot has been made of the idea that a shorter case provides for a more efficient burn. Certainly the idea that a .308 Winchester case makes for a far more efficient and some would argue accurate round than the venerable 30-06 round for this very reason. My guess is that this is more about selling rifles in the new short magnum and ultra short magnum rounds than anything else. My guess is that the marketing people are still pushing the idea, and quite successfully that a new and better rifle will make you a better shooter.
I think that they are doing a pretty good job with the powders these days. We see marginal improvements in what are becoming more and more niche market powders. But in todays world what would you expect?
 

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Discussion Starter · #4 ·
Yes.
That part is easy to figure out.

I found this simulation on AR15.com.

Colorfulness Rectangle Slope Plot Font
 

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Discussion Starter · #5 ·
Studies produced of late will clearly indicate for instance that generally speaking pistol caliber carbines chambered in 9X19 will gain a significant velocity increase over the same round being fired out of a typical handgun length barrel. While on the other hand, the .45 acp round will not. Hmm.
For what it may be worth, the 9 is a high pressure round and the 45 is a LOW pressure round.
35k pis vs 20k psi?
The extra pressure might come in handy in a longer barrel.
A longer barrel on with low pressure round might actually slow the bullet down. ?
 

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A longer barrel on with low pressure round might actually slow the bullet down. ?
Too long a bbl in any caliber can slow it down. That's not a factor of max round pressure, but a factor of how long your pressure curve is sustained. If you carried the chart above out to a longer bbl length you'd see that when pressure ran out the friction of the barrel would slow it down.

Look at 38spl or 45 Colt for examples- generally better vel through lever guns than revolvers and better vel in 6" bbls than 4." (sometimes load dependent) The relative % of gains in velocity of any given caliber may be in direct correlation with the pressure of a round but not determined by being a high vs low pressure round. Even in USMM Guy's example he notes "you do not gain any significant velocity increase," but there is an increase nonetheless. (until you get too long a barrel)
 
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Discussion Starter · #7 ·
Yes.

But my question was about how long the powder burns.
 

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Yes.

But my question was about how long the powder burns.
Order of magnitude is provided, I believe in post #2: powder does burn after bullet launch ... depending upon barrel-length and caliber. Very briefly ... though perhaps longer than bullet transit time. #2 shows [ very high-order ] micro-seconds: in casual-ish writing on propellent burn, at least one very knowledgeable author, uses milliseconds. Powder burning while exiting the barrel is going nearly the speed of the bullet and rarely gets more than barrel-length from the muzzle. So call it <3ms, maybe 5?

Is that close enough for your purpose?
 

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But my question was about how long the powder burns.
I'd guess it's different in every single cartridge... depending on a bunch of variables like powder charge, load density, powder position, crimp, whether seated to the lands, etc.

Best answer might just be "not long at all!" ...lol
 

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Surely you can see, especially in film clips of large artillery pieces, naval guns and such. The huge flash of unburned gasses burning off after the projectile has left the end of the barrel. So this would indicate that yes powder having transitioned into gas is still burning after projectile launch. For a very short duration of time at least. So that leads to the question of whether it is just gas burning or is powder still burning.
And certainly any gain in velocity will be dependent on powder/charge weight and barrel length. I would be interested to know how this works for black powder?
 

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Surely you can see, especially in film clips of large artillery pieces, naval guns and such. The huge flash of unburned gasses burning off after the projectile has left the end of the barrel. So this would indicate that yes powder having transitioned into gas is still burning after projectile launch. For a very short duration of time at least. So that leads to the question of whether it is just gas burning or is powder still burning.
...
So that leads to the question of whether it is just gas burning or is powder still burning.
Because the bullet seals the barrel and pushes, effectively, all the air out: effectively all the gas that follows the bullet out is propellent; either already fully burnt or still burning. Minuscule amounts of vaporized metal. Only tiny amounts of air subtended(?) by the bullet: what my chem professors would always tell me:

- For the purposes of this experiment, you can disregard.

I was a lot of trouble to them too.

The black powder question is interesting: the above applies only to modern smokeless, which is designed to burn nearly 100% into a gas.
 

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So this brings up another consideration. Since there is very little free Oxygen in a given round of ammunition. There is a bit because we all know that most cartridge cases are not full of powder. It is understood that with compressed loads there is about zero free Oxygen available inside of a given case. So that would mean that a certain amount of Oxygen must be produced in the reaction itself. After all "burning" is just a form of accelerated oxidation. It would stand to reason that the ideal formulation would be set to where just the right amount of Oxygen is produced, and at such a rate so as to cause all of the powder to be converted into propellant gases prior to or exactly at the point where the projectile leaves the barrel. I guess that this would happen in a perfect world.
But we all know that you can take the same round and fire it out of a two inch barreled revolver and get a much bigger muzzle flash than when fired out of a six inch barrel.

I wish that Nick A had not needed to leave the forum. He knew all the answers.
 

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Some of these questions depends on if we could determine exactly when the powder is completely converted to gases. The powder grains transition from a solid to a gaseous state when it burns. All material does. Some go from solid to liquid to gas, while others transition straight from solid to gas. So when powder transitions do we now no longer consider it as powder? So therefore we consider the combustion phase over?

I'd say the combustion of smokeless powder includes the gases produced during its combustion, therefore the fireball we see exiting the barrel shows the combustion process is not over.

My $0.02
Grumpy
 

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So this brings up another consideration. Since there is very little free Oxygen in a given round of ammunition. There is a bit because we all know that most cartridge cases are not full of powder. It is understood that with compressed loads there is about zero free Oxygen available inside of a given case. So that would mean that a certain amount of Oxygen must be produced in the reaction itself. After all "burning" is just a form of accelerated oxidation. It would stand to reason that the ideal formulation would be set to where just the right amount of Oxygen is produced, and at such a rate so as to cause all of the powder to be converted into propellant gases prior to or exactly at the point where the projectile leaves the barrel. I guess that this would happen in a perfect world.
But we all know that you can take the same round and fire it out of a two inch barreled revolver and get a much bigger muzzle flash than when fired out of a six inch barrel.

I wish that Nick A had not needed to leave the forum. He knew all the answers.
Smokeless powder contains its own oxidizer. That much I do remember.
 

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I'm in agreement with RELOADER's reasoning and calculations. MY result was different, but close, b/c I used a different muzzle velocity. We might both be wrong, but I see how we both arrived at our results.

The insight of a metallurgist would not be out of place, here. It would be interesting to know if the steel used to manufacture barrels will burst if the pressure within it goes from atmospheric to 18,000 p.s.i. in slightly less than one millisecond. If bursting is likely, then our estimated combustion time is likely too short, and we're overlooking something.

OR one of us could just e-mail Hodgdon/IMR/whomever else they bought this week, and ask them.
 
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Smokeless powder contains its own oxidizer. That much I do remember.
Not exactly.
Smokeless powder is one single unstable chemical compound, nitrocellulose. Or two, with nitroglycerine in double base powder. When "ignited" they decompose with energy release into hot gases. Yes, the oxygen in the nitro- groups does react to give oxidized products, but it was not present as a distinct "oxidizer" like the potassium nitrate in black powder.

The "burn" is very fast, complete by the time the bullet has traveled only a few inches down a rifle barrel. The much smaller powder charge in a pistol cartridge is gone even sooner.

Barrel time is not a simple number, assuming a 3000 fps muzzle velocity from a 24" barrel is an "average" of 1500 fps starting from zero is a very rough approximation. If you were wild and crazy about it, you could look on Bullets By the Inch where they sawed off gun barrels an inch at a time, and break it down in to small increments for numerical integration.

Muzzle flash is commonly said to be the hot gases igniting when they hit air with abundant free oxygen.
 

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A firearm is a heat engine. A single cylinder engine with a free ( not connected) piston.
When the fuel is lit hot gas known a plasma (plasma is the fourth state of matter) is created, it burns untill the fuel is consumed.
It burns in and outside the barrel.
The pressure it creates also creates the ever increasing expansion space behind the bullet.
Keeping the expansions space pressurized at an ever increasing pressure is the key to higher MV. That why we use slow burning powder in long barrel guns. Even short barrel gun can see a MV increase with slow powders. It all a compromise.
 

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A firearm is a heat engine. A single cylinder engine with a free ( not connected) piston.
When the fuel is lit hot gas known a plasma is created it burns untill the fuel is consumed.
It burns in and outside the barrel.
The pressure it creates also creates the ever increasing expansion space behind the bullet.
Keep the expansions space pressurized at an ever increasing pressure is the key to higher MV. That why we use slow burning powder in long barrel guns. Even short barrel gun can see a MV increase with slow powders. It all a compromise.
It is not plasma.
 

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The definition of plasma, thank you MIT:

"Plasma is superheated matter – so hot that the electrons are ripped away from the atoms forming an ionized gas. It comprises over 99% of the visible universe. In the night sky, plasma glows in the form of stars, nebulas, and even the auroras that sometimes ripple above the north and south poles. That branch of lightning that cracks the sky is plasma, so are the neon signs along our city streets. And so is our sun, the star that makes life on earth possible.
Plasma is often called “the fourth state of matter,” along with solid, liquid and gas. Just as a liquid will boil, changing into a gas when energy is added, heating a gas will form a plasma – a soup of positively charged particles (ions) and negatively charged particles (electrons).
Because so much of the universe is made of plasma, its behavior and properties are of intense interest to scientists in many disciplines. Importantly, at the temperatures required for the goal of practical fusion energy, all matter is in the form of plasma. Researchers have used the properties of plasma as a charged gas to confine it with magnetic fields and to heat it to temperatures hotter than the core of the sun. Other researchers pursue plasmas for making computer chips, rocket propulsion, cleaning the environment, destroying biological hazards, healing wounds and other exciting applications."

That's what I always thought it was. :rolleyes:

Grumpy
 
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