The expolsion in a black powder barrel?

[jwh1947]

I would like to hear from someone who has a physics and/or chem. engineering background and who has formally examined this subject.  I can come up with theories myself and everybody has an opinion.  I seek scientific facts and data here.

Consider the detonation of black powder and the conventional location of the touch hole, that is, near to the rear of the barrel, close to the front of the breech plug.  You have an explosion starting at the rear and moving forward.

What if a charge were detonated with a touch hole placed nearer to the center of the powder charge.  Would you not have a faster burst, with heat moving in two directions for only 1/2 the distance and blowing the same charge?

What would this do to the pressure curve?  What would be the effect, if any, on the moving ball?  Would it be significant?

I noted that the detonators on WWI artillery shells are what we would consider conventional, at the rear, like a primer.  However the big shells used in WWII have a detonator that runs deep into the charge, with many holes.  I know, apples and oranges...different propellants and different equations, but it got me to thinking.  Can you help on this?  Wayne 

[Acer Saccharum]

I don't have any formal training in that field. If you do have the touch hole toward the center of the charge, it may indeed alter the combustion characteristics. I imagine one might experience a steeper pressure curve, with more of a bullet upsetting detonation?

Mechanically, you will end up with a pocket to collect combustion debris. But that has little to do with your hypothesis.

Tom

[davec2]

I would first point out that some of the terms you are using are not technically correct.  Back powder is a low explosive and does not "detonate" it "deflagrates".  The flame front propagates through the material at much less than the speed of sound (in the material).  A true detonation, characteristic of a high explosive, is propagated by a shock wave faster than the speed of sound in the material.  While some smokeless powders can sometimes detonate (always a bad thing in a gun barrel) black powder can not.  The difference is that low explosives deflagrate at hundreds of meters per second while high explosives detonate at thousands of meters per second.  (TNT for example, detonates at 8, 000 to 10,000 meters per second which is way more than an order of magnitude faster than black powder.)

The ignition source in artillery systems is not a detonator.  If you were to detonate the smokeless powder in an artillery piece, you would destroy the gun and its crew.  As in small arms ammunition, the ignition source in an artillery shell is referred to as a primer and it burns it does not detonate.  A blasting cap detonates and is designed to produce heat, pressure, and shock to cause a high explosive to truly detonate releasing the maximum amount of energy in the shortest amount of time.  (Exactly what you don't want inside a gun barrel.) It is true that different artillery systems use different ignition systems, but it is not universally true that the primer is lengthened and fires radially along the axis of the propelling charge.  Guns firing fixed or semi fixed ammunition (like a naval 5"-54...75 pound projectile and 15 pound propellant charge) use an elongated primer built into the shell casing.  However, bag guns (like the 16" guns on a battle ship...2,000 pound projectile and 800 pound propelling charge) use a very small primer and a booster of black powder sewn onto the rear bag in the charge.  The ignition method has to do with what the gun is designed for, the weight of the propelling charge, the type of powder used, the weight of the projectile, etc.

Bottom line, powder charges in guns are designed to deflagrate and are initiated by a primer or igniter.  They are designed to release the chemical energy they contain in a slow (relatively), controlled fashion to transfer their energy to a moving mass.  Explosives are designed to detonate and must be initiated by a detonator.  They work by shattering materials around them with the shock wave they produce.

To answer your specific question, while the ignition point (i.e. position of the touch hole) might slightly effect the characteristics of the time pressure curve in the barrel, the same amount of granulated black powder will burn at the same pressure and at the same burn rate whether it is ignited in the front, back, or middle.  My opinion, it would not make a detectable difference in something like a flintlock rifle.

[LynnC]

The very first post I ever made on ALR was on this very topic.  A lot of opinions on this topic and not much fact.

The earliest vent location tests that I know of were conducted by John Muller in England in the latter half of the 18th century.  His tests used a small mortar with three vents, one at the front of the charge, one at middle and one at rear that could be screwed shut.  For a given charge he found that the front vent threw the ball the shortest, the mid vent went mid range and the rear vent the farthest.  Thus the most efficient burn was with the rear vent.  These were signifigant range differences.  He also conducted many other interesting experiment, all artilery related.  All can be found in his book A Treatise of Artillery 1780.

Now, do I know that the results would be the same in a rifle or fowler?....No I can't.

But I suspect that similar results would found.  Based on Mullers tests, I have always place my vents as rearward as practicable to get the most out my powder charge.  Maybe I'm just a bit cheap and placing the vent near the breech plug just make me feel better

Until someone builds and chronos a three vent rifle we are just speculating.  Perhaps someone has and we just havnt heard the results.
JMHO - yall have a great Sunday.........Lynn

[BrownBear]

On the distinction between detonation and deflagration, it is possible for black powder to detonate, though probably not with conventional priming systems.

A close friend found that out the hard way.  He's a gifted machinist/metal worker and was asked to do some work on a muzzleloader barrel belonging to one of the "big names" that hunts with muzzleloaders all over the world.  My friend accepted his word that it was "unloaded" and took a torch to the breech.  The barrel literally exploded, throwing pieces of barrel (and unfortunately my friend's right thumb) all over the shop.  The barrel owner swears up and down it was a normal hunting load that he inadvertently left in the barrel.

My friend's "bad" for not double checking for a load of Goex 2f, but the result of igniting with a torch rather than a cap or prime was no deflagration.

[LynnC]

BTW - Dave and I were typing at the same time an he posted first. So I am not disputing anything Dave wrote as I hadn't yet seen it.

Again - yall have a good day!

[hanshi]

I can't speak for the placement of the vent for a black powder charge but can speak on some misconceptions that never seem to fade away.  Just because something explodes does NOT mean it has any connection to a detonation.  Aerosol cans, flour/sugar/coal/metal/etc. dusts explode.  That does not mean they detonate.  Black powder, smokeless powder, etc, DO NOT detonate nor is it possible for them to do so due to their chemical composition.  An explosive will either detonate or deflagrate depending on what exactly it is.  A barrel that explodes is just that, a barrel that explodes.  It says nothing about the nature of the explosion.  Detonation is determined by whether a substance is an HE or a LE.  They can't cross lines.  An HE (something that is capable of detonation) CANNOT be used as a propellant.  It doesn't matter how much pressure an explosive can generate. it is the SPEED of the explosion that determines whether or not detonation has occurred.  A detonation produces speeds that are exponentially  faster than low explosives.  Black powder burns at about the same speed regardless of how it is arranged.  Smokeless powders generally burn faster as their pressure increases, hence, the term "progressive burning propellants".   Their speed is still limited because they are not HE and cannot detonate.  Mentos candy dropped in a plastic water bottle will explode but not detonate.  I hope this brings a little clarity to the issue. 

[BrownBear]

I can sure recognize that different things are happening with different powders and different burn rates.  Explosion, detination, deflagration.....  Semanticize as you must, but I bet most folks can't even agree on definitions, much less use the words right.  Not my nevermind.

All I can tell you is that one of the better machinists ever born is now known as Lefty.  His thumb laying there twitching on the floor didn't really care what the event was called.

[smylee grouch]

I think one of those inline guns was making an extended nipple(inside of barrel) version that they claimed gave more performance over the standerd style. Dont know if they ever proved it one way or another though.   Gary

[Dr. Tim-Boone]

"Until someone builds and chronos a three vent rifle we are just speculating.  Perhaps someone has and we just havnt heard the results.
JMHO - yall have a great Sunday.........Lynn"

Sounds like a call for Larry Pletcher!!

[Roger Fisher]

"Until someone builds and chronos a three vent rifle we are just speculating.  Perhaps someone has and we just havnt heard the results.
JMHO - yall have a great Sunday.........Lynn"

Sounds like a call for Larry Pletcher!!

Or Mad Monk if he isn't busy pedaling his bike up and down the Lehigh River!  Those old guys need their excercise!

[LynnC]

Hi garry trapper - I think the very Zip gun you mentioned with its extended nipple that ignited the charge forward of the breech face was in that discussion that I first posted on.  It was the latest and greatest of its day and I got my feathers burnt for posting a different point of view as I recall .
I still hold the view that the most rearward vent causes the most efficient powder burn because Mullers test is the only thing I have ever seen on the subject.  I too would love to see some test results in a BP rifle.

Jus another test to ad to Mr Pletchers list :-)

[davec2]

Lynn,

The test with the 1780 mortar understandably shows more power for the lower vent ignition.  In a very short barreled device (like a mortar), the projectile will leave the bore faster than the entire charge can burn if it is ignited at the top.  If ignited at the bottom, the flame front will propagate through the propellant mass as the projectile is starting to move.  More powder will be burned behind the projectile before it leaves the tube imparting more energy.  My comments that it should not make a difference in your proposed case were for a long barreled device, like a long rifle, where all the powder will be consumed before the projectile leaves the tube no matter where it is ignited.

Brown Bear,

It is categorically NOT possible for black powder to detonate.  The difference is not semantic, as Hanshi correctly points out, it is a physical property of low explosives vs high explosives.  "Lefty" experienced a barrel burst caused by a propelling charge being contained beyond the pressure capability of the barrel, not a detonation.  I have, just recently, demonstrated to a group of propulsion scientists that a blasting cap (i.e. actual detonator) placed in a pound of black powder will result in blowing a lot of completely unburned powder all over the test area with little or no combustion of any kind.  Contrary to your comment, experts in the area of high and low explosives precisely agree on the difference in definitions and must use the right words.  People who do not routinely manufacture and / or work with explosives get their terms jumbled.  I say again, this is not semantics.  There is a tremendous difference between a pressure burst and a detonation.  That's why low explosives are used as controlled propellants and high explosives are used destroy whatever is near them when the are initiated.  They don't use TNT for a propellant charge and they don't use smokeless powder (or black powder) as a warhead.  If you are interested in a detailed and excellent treatment of the subject, I highly recommend a book titled "The Chemistry of Powder and Explosives" by Tenny L. Davis.  The book was written during WW2 and is an excellent treatment of the subject.

Hanshi,

Excellent post, but one slight error - some smokeless powder can indeed detonate.  In the same demonstration noted above, I placed another blasting cap in a pound of Bullseye pistol powder.  The complete and true detonation was easily observable as the blast wave hit the observers.  Bullseye can do this because it is a double base powder, a mixture of both nitrocellulose and nitroglycerine.  Nitroglycerine, being a high explosive in itself, imparts denotability to double base mixtures and can propagate a very high velocity shock wave through the explosive mass.  This sometimes happens inadvertently in cartridge loads that have too much air space in the cartridge above a small powder charge and can result in destruction of the firearm.

[Larry Pletcher]

I got in on this discussion late, having been to the National Shoot and am still getting stuff put away.  I have no unique experience to add to the detonation part of the discussion and appreciate the chance to learn.

Testing the location of the vent in relation to the charge may be a workable experiment.  I need to do a little thinking on this.  I'd like to see if this has already been done in a rifled barrel before adding multiple vents to an existing barrel. 

I also have a couple of fellows I like to run ideas past before starting a new project - kind of a "Pletcher's Think Tank" if you will.  These fellows have added insight and helped with methodology.  Good science should be is repeatable, so it's worth the time to plan well.  Could be fun.
Regards,
Pletch

[Daryl]

Frontal ignition was used during the second war- at least in experimentation at Frankfort Arsenal At the forfront of this was Julian Thatcher and Elmer Keith along with Townsend Whelen and Phil Sharp, I believe.  Their work was mostly in .5 and larger ammunition and they were said to obtain some wonderful presure curves and higher velocities with lower resulting barrel temperatures. The lower temperatures were due to more of the powder being burned in the case (or breech) itself, utilizing the expanding gas alone to push the bullet down the bore rather  than the bullet plus unburnt powder behind it being pushed down the bore by gases in the rear.

Elmer own experimented with this front ignition concept in the .280 Dubiel, Lorane's (his wife) rifle and 'noted' a cooler shooting barrel and higher velocity, ie: lower trajectories as not many businesses had chronogrpahs, let alone private citizens.  They called this "Duplex Loading", although it had nothing to do with using 2 different powders in the same case.

In the 1990's a Precision Shooting magazing had an article on Elmer's old "Duplex" loading - in that with the use of a long tube (Elmer's idea from Frankfort) from the rear, the powder charge was ignited very near the top of the powder column.  This 1990's writer did have a chronograph- (doesn't everyone have at least one, nowadays?) and also experimented with different burning rate powders, one above the other, true duplex loading. His rather extensive results (for a private citizen) shows absolutely no advantage to the forntal ignition nor from the use of different burn rate powders in layers inside the case.

 What does all this have with this thread?

It shows the idea of frontal ignition was and is used today - but seems it is only useful in cannon - like the huge ship and battery monsters of WW11.  Perhaps frontal ignition is used in modern Artillery - I don't know.

That the idea or concept is still alive is rather interesting.

[LynnC]

Good Morning Guys,

Dave-Your comments above sound very reasonable.....

I would love to see the vent location debate settled - Let the testing begin!

Larry - I would think a simple straight screw-in vent and 2 screw-in plugs would be sufficient and maybe test fired from a bench and vise.

If you chose to do it I would be most interested in the outcome whatever it may be.  Thanks for all myth busting you do!

[Daryl]

Yeah - it's GREAT to have Larry on this forum.

[Mad Monk]

There are times when you can get black powder to MIMIC true detonation.

In a closed tube.  If you apply heat and the entire mass of powder is heated to the ignition point of the powder the entire mass ignites at once.  The results mimic true detonation but it is still not true detonation.

There is a Bureau of Mines report from the 1940's that describes a large amount of "damp" black powder being stored in a hot magazine.  A chemical reaction began in the powder that involved the sulfur and the potassium nitrate.  Which evolved heat.  Once the ignition temperature was reached the entire mass ignited.  This involved blasting powder that had been deliberately made wet for blasting work.

If you apply the flame from a torch on a barrel with a charge and a projectile in it you can get the same effect.


The BP cartridge boys played with ignition at the base of the charge in a cartridge versus a tube directing the primer flame to the front of the chasrge.  Rear versus charge front ignition.  It proved nothing in the gun.


With a flinter or percussion gun and black powder.

In a normal charge the source of ignition ignites a small amount of powder.  The hot gases and hot debris moves up through the charge in the spaces between the powder grains.  With a fine grain powder this rate of flamespreading can be up around 2,000 feet per minute through the charge.  In most loadings the entire mass of the charge has been ignited before the projectile has materially moved off, or away from, the charge.

Nobel & Abel discussed this in one of their papers.

E. Ogre

[jwh1947]

Special thanks to davec2 and others who have offered specifics on this issue.  I, for one, am learning something about physics and appreciate the definition of terms and clarification that has been given.  This is what I asked for, and the site is providing it.

Using dumb Dutch logic, I would posit an answer to my own question about significance.  If a different touch hole position would yield significantly better results, the oldtimers probably would have used it. 

Thanks for the information. 

[LynnC]

I would agree JWH, if there was a better vent spot they probably would have used it

Years ago I began a study of Civil War era field cannon barrel construction, both US and CS.  Of all all the tubes I surveyed only one materially deviated from the norm of vent very near the bottom of the bore, ie at the breech face.  The one exception was a cast iron and banded Confederate Tredegar foundry version of a 12 pdr Napoleon.  Its vent intersected the charge at the mid point.

I feel sure that extensive testing of vent location must have been done during the early 19th century for both small arms and artillery but I've never found reference to any records of it.

Perhaps it was so obivious to our ancestors that the vent goes at the breech that it was virtually unquestioned.

Oh, to have a modern test to settle the question........Lynn

[Mike R]

I would agree JWH, if there was a better vent spot they probably would have used it

Years ago I began a study of Civil War era field cannon barrel construction, both US and CS.  Of all all the tubes I surveyed only one materially deviated from the norm of vent very near the bottom of the bore, ie at the breech face.  The one exception was a cast iron and banded Confederate Tredegar foundry version of a 12 pdr Napoleon.  Its vent intersected the charge at the mid point.

I feel sure that extensive testing of vent location must have been done during the early 19th century for both small arms and artillery but I've never found reference to any records of it.

Perhaps it was so obivious to our ancestors that the vent goes at the breech that it was virtually unquestioned.

Oh, to have a modern test to settle the question........Lynn

on cannon--I am curious, as a canoneer, the vent hole needs to be placed so that the vent prick can pierce the powder bag--if right at the face of the breech, the prick tends to "miss" or slide behind the charge bag. Some vent holes are slightly slanted forward to ensure the prick tip hits the bag. Recently I had trouble with a repro naval cannon [and perhaps poorly 'rolled' charges] where the vent prick pushed the charge forward without penetrating the bag. In cannons, at least, I like a vent hole slightly ahead of the breech face.  Did your study find that true?

[LynnC]

Yes Mike - where the bore was unobstructed and the vent clear, the vent usually intersected at the begining radius transition from bore to breech face. Probably about an inch plus or minus from the face. I must admit not getting measurements on every gun examined.  Most in parks today are either spiked or "loaded" with trash or both.  But in this day and time it's probably a lot safer to have a totally disabled tube sitting in a park

[Larry Pletcher]

It seemed reasonable to sit on this from an experimenter's perspective,  hoping to think it all through.  The experiment is doable.  In fact I have a ruined barrel given to me that could be the basis for the experiment.  A vent could be installed just in front of the breech and then plugged when the forward vent is installed.  The forward vent would be installed just behind the ball with a normal charge. 

The unintended consequences of building a gun with a forward vent, however, make this futile IMHO.  First, smaller charges could not be used because seating the ball would likely cover a forward vent  All variations in the charge would have to be larger rather than smaller.

A far worse consequence would be the effect on the architecture of the gun.  Can you imagine a customer asking a gun-maker to move the lock forward 1/2 inch to accommodate a forward vent? IMHO such a request would be summarily rejected by all gun-makers I know.  Besides the appearance of moving the lock forward, the trigger and trigger guard need to be moved forward.  Rearranging gun parts this way on a gun with great original architecture would be unforgivable.

So, while the experiment can be done, a forward vent would create such problems with the guns shape that no maker would do it. Unless there is another reason for doing the experiment, I'll likely pass on this one. 

Regards,
Pletch

[LynnC]

Good points Larry

The only debate it would settle is that a vent at the breech is most efficient or anywhere is just as good.  If I had a chronograph I'd have satisfied my own curiosity - Thanks for considering it anyway.
Lynn

[Daryl]

A mule ear lock, ie: "side slapper" could easily accomodate this system with a longer hammer, but not any other lock I can think of.