burning


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x_wrench
April 10, 2013, 05:22 PM
i am not sure if this is the right place or not. so if not, please move it. anyway, i have been loading for quite a while. looked at many books on reloading. i guess i only partially understand the "burn rate" thing. i get how different powders burn at a different speed. but being a lifelong mechanic, i tend to view things as they happen inside of an internal combustion engine. in regards to gun powder, in my brain, this equates to fuel/air mix in the combustion chamber. obviously the biggest difference is that in a combustion chamber, there is a considerable amount of room for gasses to compress. inside of a rifle, pistol, or muzzle loader, there is little to none. that is where things get "fuzzy" for me. in slower rifle powders, the bullet moves down the barrel as the powder is still burning and gaining pressure. but i am not sure of where peak mean useable pressures occur (1/16th down the barrel, 1/4 way??) . and in muzzle loaders, with either real b.p. or substitutes and many pistols, everything happens at a much faster pace. i THINK that the bullet HAS to move somewhat as the quick powder burns, if it did not, i would think that the pressures would rise so rapidly, the gun would simply become a pipe bomb. in rifles all of this makes a certain amount of sense, pistols do the same thing only much quicker, as evidenced by the burning powder creating the flash towards dusk. black powder. i guess it the one that is the least understood by me. it can be an explosive, or a gun powder. which confuses me. in my mind, an explosive detonates, not burns. but if it detonates in a barrel, the gun should become a pipe bomb, unless the steel is extremely thick and can contain all that pressure. a cannon would be a good example of this. but in a rifle or pistol, the walls do not seem thick enough to contain a detonation. can somebody please clear this up for me?

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ATLDave
April 10, 2013, 05:35 PM
I think I broadly understand the question. Smokeless powder does not explode. It is deflagrating. This process converts the powder into a combination of gasses and soot. It also releases a lot of heat and some light. The gas occupies much more space than the powder, so it increases pressure in a closed system.

Different powders deflagrate/burn at different rates. Faster powders convert their mass into gas more quickly. Slower ones do so more slowly.

Pressure generated by burning powder inside a chamber and barrel can be graphed. A typical arrangement is to have pressure on the vertical scale, time on the horizontal scale. At ignition, pressure will rise for a time, and then fall slowly as the volume available to the gas increases; the bullet moves down the barrel and, unless more gas is added, pressure will fall accordingly. When the bullet clears the end of the barrel, pressure will drop abruptly, and the bullet's acceleration will cease.

If you've graphed the pressure as described above, the total impetus imparted to the bullet is the area under the curve. If you want more velocity for a given projectile, increase the area under the curve - but don't cross whatever threshold has been set for the max/peak pressure.

Fast powders will reach their peak pressure sooner (further to the left on our imaginary graph). Slower ones will reach it later.

Did that get it for you?

Walkalong
April 10, 2013, 06:33 PM
They are all extremely fast, some are just less fast. Slow is kind of a misnomer.

The case volume and shape make a difference, as well as the bullet weight, as far as what "speed" (Just how fast) the powder needs to be.

the gun would simply become a pipe bomb The difference being in the pressure has some where to go that is not blocked by much (Bullet weight and friction), and the powder burns and does not detonate. Powder in a pipe bomb seems like an explosion, but really isn't. The powder just burns too fast for a closed pipe to hold it.

Pressure curves matter mostly for gas action semi auto guns, where burn speed is more limited as well.

jstein650
April 10, 2013, 07:18 PM
"it can be an explosive, or a gun powder. which confuses me. in my mind, an explosive detonates, not burns. but if it detonates in a barrel, the gun should become a pipe bomb"

One can make a 'pipe bomb' with smokeless (nitro powders) but, the result is a bursting, still, not a true detonation. I have made 'pipe bombs' with black powder, with the result being all of the gas being pushed out of a 1/8" fuse hole - with a pretty big 'bang' with no bursting of the container. In the end you do have a 'burning' with the gas being expelled through a small hole with no bursting. Modern smokeless powder does much the same thing in a rifle. I think taking this concept to an extreme - shotguns- will demonstrate the dynamics. A relatively large bore will indeed see all the powder, usually very fast by rifle standards, be consumed with the payload then accelerating down the bore. Even though double base powders use nitroglycerin as a component, the treatments given to the powder do not allow an actual detonation, in which the decomposition of the powder generates a true high velocity shock wave that would travel much faster and more energetically than the bullet. As said above, 'slow' powders generate a somewhat slower acceleration compared to faster powders, but the area under the curve is more what matters in the real world as far as velocity goes. As to the question as to how far the bullet might travel after ignition, 1/4 inch, 1/2 the barrel length?? We'd all like to know...

rcmodel
April 10, 2013, 08:02 PM
A good way to understand the peak pressure curve is to look at the barrel contour on a centerfire rifle or shotgun.

The thickest part is around and just in front of the chamber when it begins to taper off to a thinner barrel section.

Another way to look at it is, where a rifle barrel burns out over time.

It begins right in front of the chamber, and progresses foreword until 2" - 3" of rifling is toasty fried and looking like an orange peel.

Inside the cartridge case is where most of it burns, and 2" - 3" forward of the chamber is where ends.
From there, the hot gas generated continues to expand and apply pressure further down the barrel.

But what starts out as 60,000 PSI in a centerfire rifle chamber is down to 15,000 PSI or so at the muzzle when the barrel is thinnest.

rc

JSmith
April 10, 2013, 08:04 PM
I found this article to be a helpful introduction to internal ballistics:

http://en.wikipedia.org/wiki/Internal_ballistics

jstein650
April 10, 2013, 08:17 PM
That is an excellent article. And sort of goes along with some of the intuition I've developed over the years of loading and thinking about, and examining what seems to happen. rcmodel's example also is a sort of good way to visualize how these things have driven the way barrels are made to deal with the pressures involved. I didn't know how the first few inches of a HP rifle bore looks, but this makes sense.

toiville2feathers
April 10, 2013, 08:22 PM
part of the pressure curve/ spike is dependent on the weight of the bullet, how much neck tension and how close to the lands of the rifling the bullet is seated. This is ,for lack of a better description is free movement. As soon as the bullet meets resistance pressure spikes.

JSmith
April 10, 2013, 08:47 PM
One of the things I've found I enjoy most about reloading is that it has made me consider what happens in those few milliseconds from hammer-drop to "bang" much more carefully than I did when I was shooting factory ammo. I've started re-learning a lot of the physics I learned in school and haven't thought about since.

Tolkachi Robotnik
April 10, 2013, 09:11 PM
Even some 'slow' powders are coated with something else to get the bullet rolling. Nitroglycerin is in a lot of different powders. Gun cotton is in others, but can also be in a powder with nitroglycerin. Those with two modes are usually considered double based powders.

A lot of this is trade secrets and some of it was worked out a long time ago.

Some of the slower powders when shot through large capacity cartridges require magnum primers, so as to get a more consistent ignition.

They really do burn, and produce their own oxidizers as they go. Burn rate is determined by how much oxidizer is available as much as the actual power of the fuel. This becomes very complex when other adjuncts are included in the mix for shelf life, cleaner burning, etc.

The actual space and pressure available can also feedback to the burn rate. Linear responses are not very common in different cartridge volumes. Most of the time consistency and accuracy is best with full cases or near full cases and complete ignition. Fire coming out the bore with the bullet usually does not help. Little pip squeaks with powder unburnt in bore does not help.

x_wrench
April 11, 2013, 07:02 AM
the Wikipedia article helps a lot. my misunderstanding of how black powder burnswas way off. i found it very interesting that they have been experimenting with RDX as a propellant. mainly because i have previously known it strictly as an explosive. THANX!

osage48
April 11, 2013, 09:27 AM
ATLdave, very good explanation!

Searcher4851
April 11, 2013, 11:17 AM
Interesting discussion and article. Thanks

JSmith
April 12, 2013, 07:53 AM
More detail on propellant burning here:

http://www.rimworld.com/nassarocketry/pdfs/031-PROPELLANT%20PROPERTIES.pdf

x_wrench
April 12, 2013, 05:58 PM
http://www.rimworld.com/nassarocketry/pdfs/031-PROPELLANT%20PROPERTIES.pdf

wow, that, at least to me, is intended for rocket scientists. to much of it is way over my head. i would have to print the article, get a dictionary, and rewrite the article so i could read it and maybe understand it.:banghead::banghead::banghead:

JSmith
April 12, 2013, 10:32 PM
The main thing I got out of it is that the fastest powders are those where the grains have the most surface area for combustion. Thin, flat flakes burn faster than grains with thicker cross sections.

Lagarto
April 13, 2013, 12:44 AM
I recommend the book Understanding Firearm Ballistics sub titled:Basic to Advanced Ballistics,Simplified, Illustrated & Explained by Robert A. Rinker. ISBN: 0-9645598-4-6. Published by Mulberry House Publishing

My shooting & reloading group of 5 includes two with Doctorates in Physics, two with Doctorates in Engineering, Me, a humble BSME, and then a tool and die maker/gunsmith with 50 years of experience. We all have reached a consensus that this book will answer virtually any question that a reloader or shooter may need to answer.

Additionally, with a sound working knowledge of this volume it is possible to pose effective questions to components manufacturers and get reliable answers back in a timely fashon. It is the best $25.00 I have ever spent.

JSmith
April 13, 2013, 10:11 AM
Thanks, Lagarto - my copy is on order!

119er
April 14, 2013, 02:21 AM
I recommend the book Understanding Firearm Ballistics sub titled:Basic to Advanced Ballistics,Simplified, Illustrated & Explained by Robert A. Rinker. ISBN: 0-9645598-4-6. Published by Mulberry House Publishing


+1 Your one stop shop for ballistics info

If you like a little history and intersting topics pick up Hatchers Notebook. It is dated but a really intersting read.

Ammo Encyclopedia 3rd ed. is good too. Exactly what it says it is. Probably more information than is useful!

x_wrench
April 16, 2013, 06:25 PM
I recommend the book Understanding Firearm Ballistics sub titled:Basic to Advanced Ballistics,Simplified, Illustrated & Explained by Robert A. Rinker. ISBN: 0-9645598-4-6. Published by Mulberry House Publishing

My shooting & reloading group of 5 includes two with Doctorates in Physics, two with Doctorates in Engineering, Me, a humble BSME, and then a tool and die maker/gunsmith with 50 years of experience. We all have reached a consensus that this book will answer virtually any question that a reloader or shooter may need to answer.

Additionally, with a sound working knowledge of this volume it is possible to pose effective questions to components manufacturers and get reliable answers back in a timely fashon. It is the best $25.00 I have ever spent.

i will start looking for one right away. thanks!

JSmith
April 17, 2013, 06:31 PM
And... my copy arrived today.

Overall, it looks very good. THe topics I'm interested in right now - powder properties and internal ballistics - are only about 10% of the book, but it will be fine to get started and go on from there. Thanks for ther reference!

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