Topic: COMPRESSED BLACK POWDER (W.W. Greener)

Retrieved: 12/12/2014
Last Post: 03/18/2006

I found this interesting especially in light of the recent article in "The Black Powder Cartridge News" concerning compression and its effects. I was under the impression that heavly compressed BP would act like a rocket motor. At what point does 'Detonation', as quoted by Greener below, occure? Or was the fine grain powder the culprit rather then 'detonation'? Then again, if what Greener states is true, when we heavily compress a charge we breaking the gains down into fines, as illustrated in the BPCN article, are we tempting fate?

Dick Dastardly
March 17, 2006

I've pulled bullets from some very old cartridges, and some of those I've just loaded. In both cases I had to "dig" the powder out with a dental pick. Also, there were fines in the powder charge way out of proportion to the amount in loose powder. So, yes, compression can and does fracture bp grains. I suspect that is one reason consistant compression is so important to good accuracy.

I've been working on loads that compress the powder only up to, but not beyond, fracturing grains. I've marked the loads with colored primers and it will be interesting to see the results on target and over the chronograph.

TAKAHO KID
March 17, 2006

I would suggest getting a copy of the latest "Black Powder Cartridge News" (Spring 2006) Dan Phariss has begun a multi part series on compressed black powder charges and the effects on ballistics.

Dick Dastardly
March 18, 2006

I've confirmed this already from my own bench work. Different black powders respond differently to compression and to the amount of compression. I've found that LIDU is a fairly "soft" black powder and that with strong compression it produces more "fines" than does Goex. The powder producing the least amount of "fines" for a given amount of compression, so far on my bench, is Swiss. That stuff seems to retain it's granularity under considerably more compression than most others.

My chronograph and some paper targets will tell the story, but I suspect the amount of grain crushing will cause some very real changes in the way the powder burns. I'm using my 45-70 Remington RB for the tests.

Now, for some shootable weather. I'm thinkn' tests in April.

TAKAHO KID
March 18, 2006

Hello folks. I know I left you hanging in regards to my original post concerning W.W. Greener "tamped chargers and a destoryed Fielding action 450 BPE. Bill has generously given me permission to post his response:

Regarding your thread on the Open Range Forum titled

"Detonaton Of Compressed Black Powder"

A word of caution here.

Never use the word "detonation" in relation to black powder. There are two terms used in the explosives industry. Deflagration is a surface burning of the propellant grains. The grains are ignited on the surface and burn towards the center.

Detonation is where a pressure wave travels through the mass of explosive material.The pressure wave then triggering the chemical reactions within the explosive.The pressure wave must travel through the explosive at or above the speed of sound.

In the propellant industry a propellant composition capable of detonation is to be avoided at all costs. If a propellant composition exhibits even a million to one chance of going into true detonation it is totally unacceptable as a propellant. Simply due to the number of cartridges it would be loaded in and the possible number of gun failures as a result.

There is a test in industry known as the "fall-hammer" test. A weighed sample of the explosive material goes into a holder. The holder has a 1/4" hole drilled in it. Similar to just drilling a 1/4" hole in a block of metal. This is known as the anvil. Then a snugly fitting piston goes into the hole and rests on top of the sample. Both the hole in the anvil and the piston have highly polished surfaces. This goes under a long tube mounted vertically. In the tube is a 2 kilogram weight. The tube is calibrated in inches or in metric measurements. You start the test by allowing the weight to fall in the tube from a certain height. If no explosion of the sample occurs you change the sample and go to a greater height. You want the greatest height were no explosions are heard in 10 samples and then the height where 10 drops give you 10 explosions. This data may be plotted on a graph which gives an "S" shaped curve.

Under controlled conditions this give a numerical value of the impact shock ignition sensitivity of a specific chemical composition. Test data normally being seen as foot-pounds of force. Two points here. The force is applied very rapidly to the sample and the sample is being held in rigid confinement in the sample holder. Without the rigid confinement it will take a far greater force to set it off. Black powder will crumble as the force of the falling weight is applied to it. This crushing takes up a good bit of the kinetic energy of the falling weight.

All of the technical writings describe black powder as being "relatively insensitive" to impact shock ignition. Data from the early 1900's gives foot pound values compared to other explosive compositions.

Looking at the Greener writing.

Note that he describes the cartridge in question as the 3-1/4" long tapered solid-drawn brass case.

Please note "tapered". To explain, in a way. Going back to the mid-1980's. I had a letter from a man who was shooting .45-70 Trapdoors with a few of his friends. He wanted to know if the bp sub they were using was capable of "detonation". He and some others shooting the .45-70 were playing with highly compressed charges of the bp sub in the .45-70 in Springfield Trapdoor rifles. He blew the breech block right out of one original .45-70 trapdoor rifle. Another split the rear of the barrel open. Some fired cases showed signs of extreme pressures. Bulged primers and a few case head separations.

He wanted to know what was going on.

So I loaded several .45-70 cases with the same bp sub at high charge compression. The next day I pulled the bullet from one of the loaded rounds. The powder grains had crushed and fused into a solid mass. I had to drill the charge out of the case with a hand drill. All of the cartridges showed the same thing. That the charges had fused into a solid non-porous mass in the case.

Then it dawned on me. These .45-70 cases had a slight taper. The primer fires onto the rear face of what is a solid charge. There is no way that the evolving gases can get around the solid charge in the case. No escape route for the gases. As the pressure at the rear face of the charge rises it acts to wedge the solid charge even tighter in the case. If the case had no taper the solid charge could act like a solid rocket motor behind the bullet. But with the charge wedging ever tighter in the case it cannot move the bullet because it can't move in the case. You then get very high pressures in the space between the case head and the rear face of the burning charge.

In the Greener tale He states, "was induced to employ a very fine-grain black powder of foreign manufacture".

Properly glazed/polished black powder grains have very hard surfaces. Very difficult to break or crumble. Powders not as well glazed/polished have softer grain surfaces and are more easily broken or distorted. Crushing and compacting the grains will result in the same thing seen in the compressed charges of the bp sub.

When you look at late 19th century writings you see some powders being described as "diamond grain" powders. This was a very apt description of the degree of hardness of the grains surfaces. Black powder grains go into the polishing/glazing barrel with a moisture content of around 1.5% or higher. As the powder is dried by moving air the water will migrate from within the grain to the surfaces of the grains. Arriving on the surfaces as a saturated solution of potassium nitrate and some water-soluble minerals from the charcoal ingredient.

If these grains were simply allowed to dry on cloth covered trays there would be a thin dusty layer on the surfaces. In the polishing barrel the grains are being tumbled and rub against each other with a considerable amount of pressure. As the water evaporates and deposits the potassium nitrate the crystals formed are compressed and compact to form a hard skin on the grains. Under a microscope well polished grains without graphite coating give the appearance that they had been dipped into molten glass and then allowed to cool. This glass-like skin appearance is where the term glazed powder originated. The term glazing came into use long before powder companies began to use graphite coatings on the grains.

So basically what Greener was relating was the use of a fine grain powder that when highly compressed simply crumbled and fused into a solid charge in a tapered case.

Please note that I did indeed change the title of the thread dropping the word 'detonation' Though Greener discribed the event as a detonation as Bill explains it was clearly not. (Takaho Kid)