I found and article at LoadData.com by John (Mule Deer) titled "How Smokeless Burns" and I have a few questions for him or anyone else that can help.

In the article it states the following.

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 within 4-5 inches
of bullet travel.

My questions are, How did we arrive at this conclusion? Are there lab results etc. that can be tacked to this conclusion to help understand it?

Don't get me wrong, I tend to agree with this, but there are many that do not. Quickload for example disagrees with this theory.

Theory? That's my point, is it a theory or is it a fact that can be backed up with documentation?

Thanks
Steve

That's one of the points that's VERY badly stated in QuickLoads. When QL says that (for example) 90% of the charge burns in the barrel, it certainly gives the impression that powder is still burning when the bullet exits. That's not true. What it ought to say is that 90% of the charge burns - leaving 10% that never does, of course. But that unburned powder is blown out the barrel or deposited in the bore - as we've all seen. It doesn't burn for a variety of reasons, but NOT because it was still burning when the bullet departed.

The point where the powder has completed burning is at or shortly after the pressure peak. As an analogy, the point where the logs in a campfire quit burning can be determined by the point when the temperature starts rapidly dropping - even if there is wood left over.

Thinking about a typical .308 with 22" barrel, and then my 16" .308. The short barreled gun would typically make nearby shooters leave Although the muzzle brake didn't help

so is the difference in muzzle blast purely a function of muzzle pressure, when the bullet exits?

I'm also thinking about the XP-100R that I owned in .22-250, which had about a 15" barrel. Loads that did 3700+ out of a 24" barrel were usually right at 3000 fps, which is a lot slower than one would expect. It was very accurate, but the muzzle blast was rather remarkable Between the blast, and the velocity, I sure wonder if all the powder was getting burned.

Rocky

Great explanation.

Really first class

Thanks

T

The pressure of the burned powder continues to accelerate the bullet down the barrel thus more velocity with a longer barrel. Noise is a result of the exit pressure which is higher is shorter barrels

I'm sure you meant to type "accelerate" the bullet. Unless those nasty powder gasses really do loathe the bullet, LOL!

Thanks, Rocky I corrected the post

Rocky and John have explained it correctly. Some of the following may also be interesting....

The oxygen/fuel ratio in smokeless powder is deliberately set just a little "rich". That's because if it were "lean" it would be a lot harder on the interior of your firearm because you'd have hot, unused oxygen available (burned valve). Long story short, before the bullet exits, all the available oxygen in the bore has been consumed. Still, the gasses are hot enough to glow. That's the first part of muzzle flash. The second part happens when the hot gasses hit open air, get new oxygen, and re-ignite.

Knowing when all the powder that is going to burn has burned is a bit more tricky. Powder burns from the outside of the granule inward, and we know the size of the granules and the rate of burn at pressure. So we have a really good idea of how soon all the powder is burned. The NABM software is free, and models this effect. If you work at it, you can put together loads that burn the whole length of the barrel, but practical loads don't do that.

Shorter barrels have brighter muzzle flash because the propellant gas is at higher pressure and temperature when the bullet exits.

Some powder never burns. As the powder sits in the case, the granules are touching each other, and granules burn hot enough to ignite adjacent granules. However, as the bullet starts down the barrel, the available volume is greater, and the granules are no longer in intimate contact. So further ignition depends on the propellant gas being hot enough to ignite the granules. At some point, the temperature of the propellant gas is no longer high enough to ignite powder.

Denton,

As I recall, Homer Powley calculated that with the right powder charge--the case pretty much full, and developing the pressure the powder was designed for--as much as 99% of the powder would be consumed just past the peak of the pressure curve. But some loads obviously don't qualify!

A reader of HANDLOADER got irate when I mentioned this in an article. He wrote a long letter to the magazine, which was forwarded to me. He had two reasons for knowing I was absolutely wrong: A charge of IMR3031 and a 150-grain bullet in the .30-06 produces more velocity than the same charge of IMR4350, and he kills a moose every year in Alaska. (Someday I'm going to publish an article containing letters from some readers, like Jack O'Connor did in GUN DIGEST years ago.)

So if we adopted Keith's suggestion of running a tube up though the center of the cartridge to ignite the powder from the front and then use back pressure to hold all the powder in place until it was consumed, we could eliminate fouling and boost performance?

(For the record, t'weren't me. )

A polite "no" to the Keith flash tube idea. First, the length of the tube itself will cool the primer flash enough that ignition is reduced. Second, the powder that is in contact with the cartridge walls may have enough heat transfer to the brass that those granules don't ignite. Third, the powder that's compressed by the theorized "back pressure" can then only ignite on the front surface of the compressed cake or pellet of powder, which again reduces ignition efficiency. (The same thing happens to the compressed plug of powder that gets pushed down the bore behind the bullet, almost like a wad: most of that powder never burns at all because it can't ignite except on the small surface area at the rear of the plug.)

So the nice mental image of what an ignition tube would do is completely bass ackwards to what it actually does. Just like the very common "makes sense" idea that powder burns all the way down the barrel, btw.

Learn something everyday.

'Specially if you've been studying it for more than a half century!

That sounds right for rifles.

I spent a couple of fun hours just fiddling with the NABM software, just to see what is possible. IIRC, you could get combustion the full length of a rifle barrel with a really big load of really slow powder. I couldn't find any practical loads that would do that.

Of course, if they did, there is the question of whether they would kill more moose in Alaska....



All of what Rocky said, plus it wouldn't work because the whole case is pressurized, with the propellant gas filling the space between the granules.

OTOH, I've wondered about dissolving powder in solvent, and depositing a shallow disk of solid propellant in the rear of the case that would burn longer than the granules, in effect creating a sort of duplex load that would have a component that burned longer. Just silly daydreaming, I suppose.

WHICH IS IT???

You boys, Rocky & Denton, have too many IDLE BRAIN CELLS rattlin round lookin for something to play with....

OR

Your brain cells are PRESSURIZED in that case we call a cranium and the static electricity caused by them RUBBING together create sparks us NORMAL human beans never see in the UNlight of ignorance.



Seriously, I appreciate YOU GUYS and your abilities to verbalize these things in UNDERSTANDABLE terminology.

THANKS
Jerry

If I recall correctly, Keith's tube was perforated and contained black powder. Got an additional 100fps but not adopted.

Would anyone know if this was an attempt to stop hang fires when the .50 Browning was fired at a high angle?(anti-aircraft)

Yep, those are definitely compressed loads right there!

I'd need a drop tube to get that many brain cells into my undersized brain...

I believe that the idea of frontal ignition in small arms came from artillery shells

True, a lot of artillery rounds (those with brass cases) have long, perforated primer tubes. And larger artillery, with bagged charges and no brass cases, sometimes use a bag of black powder as an ignition booster. But I don't know of any that use both together - subject to correction by somebody who has been an actual cannon cocker, of course.

Keith's tube used in the frontal ignition system was not perforated, nor was it filled with black powder. He wrote a pretty good description of it, with some commentary, about 40 years later in his Gun Notes column in Guns & Ammo:

Link: Keith - Guns & Ammo October 1982

The system in fact worked as Keith and co-workers described it, producing lower pressures, higher velocities, and lower barrel temperatures. However, it was impractical, involving too much fiddle-dee-dee.

The linked article describes a shortcoming that is rarely discussed in connection with the system: The loading requires a case-filling load of slower powder, and the cartridge case must fit the rifle's chamber very closely, to allow minimum expansion when fired. If the case expands very much when fired, that would "let the flash of the primer come back around the charge and fire it much to fast, causing a dangerous overload". One of his experimental tube cartridges in 50BMG wrecked a Frankford Arsenal pressure gun when it was fired in a loose-fitting chamber.

Hatcher at some point wrote that the flash tube concept had been used in artillery shells for some time before Keith et al. began their experiments.

--Bob

I know a few guys that played with frontal ignition in rifle cartridges a few years ago and yes it did lower barrel temps, but the chamber temp actually increased and the pain in the but of the threaded tube. It worked as Keith described according to them

Bullshooter. The case usn't expanded yet when the primer "flashes."

And shorten the war by a minimum of six months.

hawkins-
I was quoting Keith's narrative. However, I had a similar sort of reservation as yourself as I did so.

In mild support of Keith's idea about relatively loose fit of case and chamber being a problem was his apparent prediction of the over-pressure event before it happened. Of course it's possible, perhaps probable, that the event occurred for reasons other than Keith's prediction.

Related to this is a general question of the pressure developed in a case with primer ignition alone. It would be helpful to know how much pressure a primer produces in a rifle cartridge case before powder ignition. It may be enough to result in some case expansion. Are data available to answer this question?

--Bob

One can estimate the progress of the burn using a plot from Pressure Trace along with a table of the burning rate of nitrocellulose at pressure. I went through this exercise with a 7 Rem and found only about half the charge is burned at peak pressure with the rest several more inches down the bore. QuickLoad--which uses a different math model of the burn--agrees.

How does it develop peak pressure with only half of the charge burned?

At peak pressure, the volume behind the moving bullet is such that half the charge is enough to reach the pressure limit.

At this same point, the bullet is moving fast enough that the ever increasing volume behind the bullet more than accommodates the gases being created by the rest of the charge. Another way of looking at this: the second half of the charge is striving to keep the pressure near the peak level.

Denton -

I've been at the reloading, powder stuff since 1975. Read a LOT of info pertaining to ALL SORTS of related components.

I've never SEEN nor HEARD that explanation. THANKS!

I know/understand the principle from Hi performance, 2 stroke engines and race cars. You CAN get the fuel mixture TOO LEAN for reasonable length of service.

I've never heard that THEY could 'injun eer' gun powder that way.

My daughter's husband is a chemist, the son of a chemist. We got to fiddling with a black powder substitute (which showed a lot of promise). In the course of that, I mentioned that the substitute was still leaving a little carbon residue. The senior chemist allowed that it was easy to get a little more oxygen in the mix, to get rid of that. It was then that it clicked: Smokeless powder runs out of oxygen before it runs out of fuel (re-ignites when it hits air), and it leaves carbon residue, just like a "rich" engine. And that's better than running "lean".

Denton-

Very Interesting.

THANKS

AGAIN.

Spread a clean big tarp out in front of ones bench, torch off a round, and sweep up the residue.

Back when I shot pistol at an indoor range on a weekly basis, I one day had a target fall off its clips. Since there was no one else shooting, I ducked under the counter and went to retrieve it. I was amazed by the crunch beneath my feet.