Home Forums Hunting & Shooting Ask The Gunwriters The Article "How Smokeless Burns"?

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.