Powder Burn in Chamber or Bore?

[steve4102]

I keep reading different opinions on this and I could use some clarification from the experts here.

Some say that powder continues to burn all the way down the bore and the muzzle flash from short barreled rifles is that "Burning" powder exiting the muzzle and continuing to burn.

Others say that all the powder that is going to burn is burned up in the chamber and the first few inches of the bore. Muzzle flash is not burning powder, but the gasses that were created by the burned powder igniting after they exit the muzzle.

Still others say that it is both. Most of the powder that is going to burn is burned up in the first few inches of the bore, but there is still a certain % of powder that burns its way down the bore. The small percentage of powder and gasses is what causes muzzle flash.

OK, which is correct and is there a link or a document anywhere that can support the correct opinion?

Part two.
It is often said that shorter barrels perform better(higher velocity) with faster powders.

It is also said that the powder that gives the highest velocity in a longer barrel will also give the highest velocity in a shorter barrel.

Which is correct?

[csmsss]

If the gases were going to burn, why wouldn't they burn in the barrel? What combustible gases would they be in the first place? And if it's oxygen you're talking about, oxygen isn't combustible. It merely provides fuel for those things that DO combust, to combust more efficiently.

[Brian Pfleuger]

As with most things, there is no absolute.

In most instances, powder continues to burn all the way down the barrel and out the muzzle. There aren't many instances (they do exist) in rifles where the entire, 100% charge is burned inside the barrel before the bullet exits. QuickLoad can give you predictions of which ones will under what circumstances and there's plenty of examples where you DO get 100% burn but it's the exception, not the rule, and I know of NO instance under normal circumstances where the powder burns 100% inside the case. Trail Boss under jacketed bullets in a rifle cartridge comes close, but even then the bullet (and some powder) moves a few inches before 100% burn is complete.

On barrel length, it is GENERALLY true that the powder which produces the fastest speed in a long barrel will also produce the fastest speed in a shorter barrel. This holds almost universally true until the length difference gets extreme, not an inch or 2 or 3 but 10 or 12 or 15 or more.

You've basically got three "zones".

Long barrel, slow powder makes fastest speed. SUPER short barrel (I mean like 2 inches) and some fast powder makes fastest speed. As the long barrel gets shorter and the short barrel gets longer, the two speeds get closer and closer until they eventually meet and cross. Where that is, there are too many variables to pinpoint without specifics.

[steve4102]

If the gases were going to burn, why wouldn't they burn in the barrel?

One opinion is that the gasses behind the bullet have no oxygen to "Ignite". Without oxygen there is no flame. The flame comes when the gasses enter the atmosphere.

[wogpotter]

The oxygen is contained within the powder or it wouldn't ignite in the first place. Most chemical compounds ending with the "ate" suffix have oxygen chemically bonded into them. Examples ammonium nitrate potassium perchlorate & so on.

If you look at high speed photographs of muzzle flashes you can usually actually see burning "sparklers" of burning powder easily. Its just too fast for the unaided eye to record normally.

[Brian Pfleuger]

Yes, the powder burns because it has it's own oxygen. However, when those high-pressure gases reach the atmosphere, they suddenly have MORE oxygen. There's absolutely no question that the powder continues to burn down and often times out the barrel under most circumstances. As I said before, there are exceptions but they only prove the rule.

[csmsss]

One opinion is that the gasses behind the bullet have no oxygen to "Ignite". Without oxygen there is no flame. The flame comes when the gasses enter the atmosphere.

So what are these gases? This shouldn't be a matter of opinion - it's a simple problem of chemistry. When smokeless powder burns, what gases are formed as a result?

[Jim Watson]

The primary flammable constituent of powder gas is carbon monoxide. There is not enough oxygen in the nitro moiety to react all the carbon in the nitrocellulose and nitroglycerine to carbon dioxide. Otherwise there is some carbon dioxide and a good deal of nitrogen. There is likely a little nitric oxide or other NOx but not much; CO and CO2 are favored.

Smokeless powder doesn't really "burn." It is made up of one or two unstable chemical compounds, nitrocellulose and nitroglycerine, that decompose by deflagration with release of heat and gas when initiated.

Black powder can be considered as burning because the potassium nitrate oxidizes the chemically and physically distinct carbon and sulfur in the powder.

[Jimro]

With all the research I've done into front ignition reloading, I've never heard reduced muzzle flash as one of the benefits.

Frontal ignition uses a tube to connect the primer to the very front of the powder column, so that when the primer is struck it lights off the powder at the base of the bullet first, so the powder column burns backwards towards the rear (instead of from the rear to the front).

This is supposed to keep the powder in the case instead of burning in the bore, and anecdotal evidence says that this is the case (the front ignition brass comes out of the rifle hotter than normal brass).

Then again, not too many handloaders bother with frontal ignition, so maybe reduced muzzle flash is one of the benefits but nobody has done the low light studies to test it.

Jimro

[57K]

steve4102, what you need is a Lyman manual where these questions are answered. The more relevant question is the distance a bullet travels in the bore before peak pressure is achieved. I've seen a good number of people arguing that peak pressure occurs near instantaneously upon ignition, or in the case of revolvers, peak pressure occurs before the bullet has left the cylinder. The QuikLoad ballistic software can be very useful as it will predict bullet travel distance to pressure max. and the amount of propellant burnt. In most cases, the slower a powders specific burn rate is, in a particular cartridge rather than just looking at a burn rate chart, the longer the distance/time will be until peak pressure occurs. That eliminates the possibility that powder is completely burned in the chamber. Distance to peak pressure is obviously shorter and quicker in handguns than rifles because of the much faster burning propellants used.

[FrankenMauser]

Smokeless powder doesn't really "burn." It is made up of one or two unstable chemical compounds, nitrocellulose and nitroglycerine, that decompose by deflagration with release of heat and gas when initiated.

I'm not trying to be a jerk, Jim, but I don't think your definition of deflagration matches those the rest of us use. What you are describing would be more appropriately called 'detonation'. However, smokeless powders are designed to deflagrate. Detonation in a firearm usually results in unintended high speed disassembly (catastrophic failure).

Wikipedia:
"Deflagration [1] (Lat: de + flagrare, "to burn down") is a term describing subsonic combustion propagating through heat transfer; hot burning material heats the next layer of cold material and ignites it. Most "fire" found in daily life, from flames to explosions, is deflagration. Deflagration is different from detonation, which is supersonic and propagates through shock." [emphasis mine]

Farlex dictionary:
"def·la·grate:
To burn or cause to burn with great heat and intense light."
"deflagration - combustion that propagates through a gas or along the surface of an explosive at a rapid rate driven by the transfer of heat"

Merriam-Webster:
"deflagrate:
to burn rapidly with intense heat and sparks being given off"


Compare that to "detonate":
Merriam-Webster:
"detonate:
to explode with sudden violence"

Wikipedia:
Detonation involves a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations are observed in both conventional solid and liquid explosives,[1] as well as in reactive gases.
...
In terms of external damage, it is important to distinguish between detonations and deflagrations where the exothermic wave is subsonic and maximum pressures are at most a quarter of those generated by the former. Processes involved in the transition between deflagration and detonation are covered thoroughly for gasses by Nettleton.
...
Unintentional detonation when deflagration is desired is a problem in some devices. In internal combustion engines it is called engine knocking and causes loss of power and excessive heating of certain components. In firearms, it may cause catastrophic and possibly lethal failure." [emphasis mine]


The fact that burn rates can be controlled by granule size, shape, and density, should be a big hint that it's deflagration, not detonation.

[Jim Watson]

I was using "deflagration" in the sense of the explosives and propellants texts that I used in my work; not general dictionary definitions.

But if you want to stay in Wikipedia;
"Combustion /kəmˈbʌs.tʃən/ or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species."

Smokeless powder does not HAVE a fuel or an oxidant.


But that's ok, I have been known to use the common vernacular "burn" for smokeless powder action just to keep discussions on track. I only get carried away with jargon occasionally, it is not a daily "clip vs magazine" moment.

[steve4102]

Thanks guys, but I think I answered my own question.
I found an article at Load Data.com written by John Barsness of Handloader and Rifle Magazines, titled "How Smokeless Burns".
I will link the article here, but I think only members of loaddata.com will be able to view it.
http://www.loaddata.com/articles/PDF...20LR%20(2).pdf

Anyhow this is some of what he had to say.


One of the most frequently
encountered misconceptions
in handloading is that
a charge of smokeless powder is still
burning when the bullet (or shot
charge) exits the muzzle. As “evidence,”
many shooters cite the muzzle
flash, especially visible in dim
light. Nope, that ain’t burning
powder. Instead it’s the hot gas produced
by burned powder, re-igniting
once it strikes the oxygen in the
atmosphere.
Instead, almost all smokeless powder
burns within a short distance in
front of the cartridge. The exact
point varies with the powder’s burning
rate, the cartridge, the projectile
etc. But even in huge “magnum”
rifle cartridge, over 99% of the
powder is burned burned within 4-5 inches
of bullet travel.

[Brian Pfleuger]

Well, QuickLoad disagrees with that assesment pretty strongly in most cases.

For instance, if I look at a .308Win (which is very close to an optimally efficient cartridge) with a 24" barrel and shooting a 180gr Hornady SST, I get the following:

IMR3031, 100% burn, occurs at 11.8"

Win748, 100% burn, occurs at 20.8"

Top velocity, RL-17, 99.46% burn

Note that the 180gr is a relatively heavy bullet, which aides combustion quite a lot. Also note that the distance is "bullet travel", not barrel length, so the barrel length is +OAL.

If I look at a much less efficient cartridge, like .243Win, shooting a lighter for caliber bullet, such as a 65 V-Max, I don't have a single powder in the "Top 10" that exhibits 100% burn before the bullet exits and only 3 of the top 20 get to 100%.

Now, they're all relatively close to 100% burn at bullet exit but they range from about 92% up to 99.7% or so and that's at bullet exit time.

It is true that the majority of powder burns in the first few inches of bullet travel but it's certainly not "100%". For example, QuickLoad says that the 65gr V-Max over Rl-17 will burn 95% of the charge at 12.11" travel (14.6" barrel length) while a max charge of H414 (3rd of the velocity list) burns 95% at 17.5" (20" barrel length). If I pick one that DOES get 100% burn, it's Win748, which is 14th on the list, it reaches 100% burn at 20.5" travel, which is 1" before the bullet exits.

Handguns are a different monster entirely. Some of the more popular loads for some cartridges don't even burn 90% of the powder.

[Slamfire]

This is a pointless and fruitless argument . This chart shows pressure in the barrel as the bullet leaves. That tells me some gas is being produced by burning powder, though the production of gas has dropped.

No combustion process is 100% so unburnt and partially burnt powder is coming out of the muzzle.

I wonder what constituents in the “hot gas produced by burned powder, re-igniting once it strikes the oxygen in the atmosphere” are not unburnt powder particles?

[steve4102]

Yup. I'm aware of QL data on this.
This is from a guy that goes by Rocky Raab and is some kind of author. I pulled this from the Shooters Forum, were UncleNick is a Moderator as well as here. Maybe he can shed some light on these different opinions.

Actually, that's one of the major points on which I disagree with Helmut Broemel (the author of QuickLoad.) The program has an output line that predicts percentage of charge burned before muzzle exit, implying that powder burns the whole length of the barrel. No other professional ballistician believes that, as far as I know - and I've asked a bunch of them.

[steve4102]

I wonder what constituents in the “hot gas produced by burned powder, re-igniting once it strikes the oxygen in the atmosphere” are not unburnt powder particles?

A solid (powder) as opposed to a gas.

[Brian Pfleuger]

I can't speak for UncleNick but I think there's two different concepts being confused in this thread.

There's "Does the powder burn down the barrel?" and there's "Does the powder burn before the bullet exits?"

Not the same thing. The powder is not necessarily "chasing the bullet" down the barrel so that there's powder burning at a location that's 20" down the barrel but when the bullet is at the 20" mark, the powder IN THE CHAMBER is still burning and the GASES are chasing the bullet.

I certainly believe it's not 100% either. Some powder goes down the barrel, some gases stay in the chamber. Most powder (and most of what is unburned at the time) stays in the chamber until after bullet exit.

I could be wrong, but that's my understanding.

[SL1]

Powder "burning" may (or may not) essentially cease as the bullet travels down the bore due to drop in pressure, BEFORE all of the powder is burned. That happens because the rate at which the flame front advances through the powder kernals is a function of the pressure in the gases surrounding the kernals, and that pressure is dropping as the bullet moves to make more space for the gases and the powder does not burn fast enough to keep pressure up (after the peak).

In revolvers with slow-burning powders like 2400 and 296, it is not uncommon to find amber-colored kernals of unburned powder left in cases, barrels and on the table/floor in front of the shooting position, usually when using those powders for less than full-power loads. In fact, W-296/H-110 is notorious for "squibbing-out" and leaving the bullet in the bore, as well, when the pressure from too-light charges never gets high enough to keep the powder burning.

So, it is possible to shoot unburned powder out of the muzzle, which does NOT light when it reaches the air and more oxygen.

On the other hand, some faster powders like Power Pistol are notorious for muzzle flash, even though QuickLOAD calculates that they are 99+% burned in a revolver with a 6" barrel.

So, it is possible to get a lot of muzzle flash when only the resulting powder gases reach the muzzle.

And, when the barrel is short enough and the powder is slow enough, it is possible to shoot burning granuals of powder out of the muzzle along with the gases.

"Flash-suppressed powders" are formulated (with additives) to make the gases that reach the muzzle essentially non-flammable in the air where they are exposed to oxygen. So, I am assuming that MOST of the muzzle flash is normally the combustion gases of the powder burning when mixed with the oxygen in the air outside the muzzle. But, there are certainly other potential contributors.

SL1

[Jim Watson]

This chart shows pressure in the barrel as the bullet leaves. That tells me some gas is being produced by burning powder, though the production of gas has dropped.

It doesn't tell me that.
50,000 psi in the chamber is not going to be reduced to atmospheric by expansion into the barrel as the bullet travels 24" down a very small hole.
For that matter, you can pump up an air gun and it will have a report as the pellet "uncorks" the residual pressure as it leaves. Nothing was burning there at all.

On the other hand, I don't doubt that it is possible for some unburnt granules of powder to exit the muzzle. A gunshot is a non-steady state process and very few reactions will go to completion in the time available in a rifle.
I just don't think they are a big part of muzzle flash and blast.

Before Quickload, before smokeless powder, it was recommended to shoot your Kaintuck over snow and look for unburnt powder which would indicate an inefficient overcharge.

[Jimro]

So far I've discussed front ignition loads which in theory eliminate powder burning in the bore not reducing muzzle blast.

Now I'm going to remind people that using an ultra slow powder like WC872 with a light bullet can often leave unburnt grains of powder in the bore. So yes, powder does get pushed down the bore from rear (normal) ignition cases.

How quickly that powder being pushed down the bore burns is a function of burn rate, bullet accelleration (the easier the bullet is to accelerate the less pressure it takes to move the bullet), and changing volume (as the bullet goes down the bore volume increases, as the bullet goes faster volume increases faster).

So yes, powder does burn in the bore. Use a slow enough powder and you can see it in the snow as previously mentioned or you can find it in the bore.

Jimro

[steve4102]

I believe there is a difference between unburned powder being pushed down the bore and powder burning all the way down the bore.

[Jimro]

Steve4102,

I believe there is a difference between unburned powder being pushed down the bore and powder burning all the way down the bore.

When you can articulate that difference please let me know.

Let me make my point a second time in a different way.

IF an ultra slow powder gets pushed down the bore during the firing cycle it stands to reason that a powder is always initially pushed down the bore during the firing cycle. If a powder is always pushed down the bore (from normal ignition) and powder is not left in the bore then the powder must be burning in the bore. If a powder is in the bore, and burning in the bore, then the question remains only how much of the powder is burnt before the bullet leaves the muzzle.

In the case of an ultra slow powder, enough to leave evidence. In the event of a fast powder, not much if any at all. My previous referrence to frontal ignition cases should help illustrated the point.

Jimro

[Brian Pfleuger]

Originally Posted by Jimro

When you can articulate that difference please let me know.

The difference is simple.

I think most of the burning/unburnt powder remains in the case/chamber until after the bullet exits the muzzle, at which point the rapid decompression pulls it forward.

There's really no reason why the powder would go flying down the bore during the initial burn. Some of it might, but it's not going to be pushed the same way the bullet is, pressure can get past a piece of powder, it can't get past the bullet. The building pressures would be more or less equal from all directions on a single powder grain. It started stationary, the only source of movement was the primer blast and the bullet is essentially still stationary when that event ends so the powder has no where to go.

That's entirely different than being 100% burned though. QuickLoad predicts 80% burn at this point, 90% at that point, but that doesn't mean the remaining powder is following the bullet, as if at that point that 90% is burned the other 10% is right there with the bullet. It's sitting in the chamber burning and the gases it produces are pressurizing the system.

Now, I don't know the exact chemistry of gunpowder combustion. I don't know if it's a single stage process or 2 or more. If it's single stage, solid to gas, the end, then most of the entire process happens in the chamber. If it's 2 or 3 stages, solid to gas, gases combine with other gases, etc, then I'm sure the entire process is happening all the way down the bore, to a greater extent in and close to the chamber and being more and more complete as it approaches the muzzle.

Of course, one might ask where we would define the end of the process. Is it the useful portion or does it continue if there's any reaction remaining, whether it's intended or useful or not? In other words, the "muzzle flash" could be considered part of the "powder burn" but it serves no useful purpose, it's basically an "accidental" result of the chemical process and is more of a by-product of the intended purpose. Does it count?

Here is an example of QuickLoads predictions. This is a 65gr V-Max and W748 in 243Win. The prediction is 100% burn, completed at approximately 23" barrel length, 20.5" bullet travel.

[DoesItGoBang]

The answer to the powder staying in the case can easily be proved (not cheaply).
- Start in an indoor range with a clean floor in front of the firing line
- Choose your favorite firearm of choice
- Shoot 1K+ rounds at a target
- Observe what is on the floor in front of the firing line (not the brass but the powdery residue)

With most ammunition and a short barrel you will end up with a nice layer of gun powder covering the floor. Increasing the barrel length or use faster powder will cause the amount to be reduced. Try it with a SBR, fireball and all, and the powder will still be there. Be careful, the residue will start a range fire. You learn through your experiences.