TAPERED CASES, LOW QUALITY POWDER & COMPRESSION

[TAkaho kid]

I originally posted this over on the Open Range Forum but I figure you folks might find it interesting. Please read down for an excellent explanation by Bill Knight.

W.W. Greener, The Gun and its Development – Ninth Edition page 570:

"When the explosive is confined by 'tamping' the pressure will rise very rapidly and the velocity of propagation may give rise a shock capable of detonating a portion of the mass. This is no doubt, the case with long charges of small-grained powder ignited at the rear.

A characteristic example of this form of explosion  came directly to the authors notice with a 450 single 'Express' rifle,.........chambered for the 3-1/4" long tapered solid-drawn brass case for a charge of 125 grains of No. 6 rifle-grain gun powder and a bullet of 260 grains. The owner..........was induced to employ a very fine-grained black powder of foreign manufacture.......and to try 4-1/2 drams or the full charge. After firing several shots at a target, another similar cartridge blew the rifle into fragments............

The Cartridges were tested, and found to give normally thrice the pressure obtained with rifle-grain powder fired under the same conditions.........."

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A picture of the shattered rifle was shown on page 571

I recieved the following response from  Bill Knight"

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.

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[sundance44`s]

That is good reading .. it explains why shouldered cases wern`t used untill the invention of smokeless powders . i often wondered about that .. i know a pard thats been trying to load a 30/30 with black .. with no good results .. the shoulder on the cases could be the problem .. i`ll have to share this info with him .

[TAkaho kid]

That is good reading .. it explains why shouldered cases wern`t used untill the invention of smokeless powders . i often wondered about that .. i know a pard thats been trying to load a 30/30 with black .. with no good results .. the shoulder on the cases could be the problem

Actually shouldered cases were around since at least the late 1860's. Remember Sharps offered the 40-70bn (1869), 40-90bn (1873), 44-77bn 1869) and 44-90bn bottle necks. In addition the 577-450 Martini Henry is a early bottle neck as well as the 43 Spanish. The big issue with bottle necks was the hard fouling forming at the case mouth. Otherwise they were very powerful and effective. The 40-90bn survived through the model 1878 Sharps-Borchardt.

However, as illustrated by Dan Theodore in the latest issue of the "Black Powder Cartridge News" he explains a few very simple techniques for dealing with the big bottle necks. (Dan is planing to campaign a 40-90 bn in long range BPCR) Incidently thats a case 2-5/8" long with the same head as a 45-70. It holds a full 90 grains under most bullets with very little compression. Its capable of pushing a 400 gran bullet at well over 1440 fps.

Several rules for loading Bottle necks with BP are:

No or light compression

Wad should never be at or below the junction of the neck and shoulder

Larger grain slower burning powders work better (1F for instance)

Cooler Primer

A good wad to protect the bullet base (far more important in a bottle neck v. a straight case)

[Triggerlock]

It would be nice if someone were to translate them articles into English so this dumb-*** from Iowa could have a chance to understand what the heck they were saying

[El Paso Pete]

Thanks fer postin this TAkaho kid.  This interesting.

[TAkaho kid]

It would be nice if someone were to translate them articles into English so this dumb-*** from Iowa could have a chance to understand what the heck they were saying

Basicly its this:

Cheap, poorly glazed and polished black powder can become fused into solid mass when heavily compressed. If you could get it out of the case in one piece it would look Similar to a pyrodex pellet. Good powder, which is glazed and polished properly, is more resistent to crushing. In fact it will actually give an audible snap if you try to break a grain in two. Poorly glazed and polished powder will simply crumble into dust like dry clump of Iowa dirt. (As kids we use to have dirt clump fights - real cool) Properly glazed and polished powder when rubbed squeezed between the fingers it will not crumble. The grains will have hard sharp edges as well.

As Bill explained; when fired, the powder burns from the bottom of the case forward. as this happens the solid plug of powder gets wedged because the case is tapered. With no place for the rapidly expanding gasses to go so you end up with very high local pressures which can go Boom as happened to the nice 450 BPE that Greener wrote about.

I hope this helps!

[Triggerlock]

Thanks for dumbing it down for me .   Let's see if I'm understanding what is being said.

No compression = maybe bad

Some compression = good

Too much compression = very bad (depending on the quality of the powder)

So.........Where does plain old Goex 2F fit in?

[sundance44`s]

sounds like problems could arise if`in ya try and push an elephant through a key hole . 

[TAkaho kid]

So.........Where does plain old Goex 2F fit in?

Well again each and every powder is different....and.... its diffrent in each type of cartridge. Its simply testing until you get a combination to work. Typically the rule of thumb is 1/16" -1/8" of compression will get you in the ball park. However you may need to taylor that for each type of powder and cartrdige. For instance, Some folks report that Swiss does not like to be compressed while Goex does, KIK or Schuetzen my like something diffrent or in between.

Its simply a matter of shooting and testing till you get what you like. I think this is one of the hardest thing for folks use to smokeless have to come to grips with. For instance, when I wanted a load for my sons 405 WCF i simply looked in an older loading manual and followed the recipe  - to do otherwise could invite disaster - With black powder The combinations are endless - bullet designs, powders, primers, granulation, lube etc, etc.all of it up to the individule to experement with. Its an endless recipe.

Its like custom cabinets: They may fit in your kitchen but not worth a hoot in mine.

Dan Pharises (sp) is currently running a great series of articles in "The Black Powder Cartridge News" on the effects of compression. The BPCN is a great magazine. Its not just about BPCR. (Incidently many of the BPCR technics can be applied to CAS) They also run articles on long range Lever gun, single actions, collecting, Shuetzen, how to's, etc. Its a good read.

[TAkaho kid]

TK - How do I get the BPCN periodical?

www.blackpowderspg.com

Click under products.

You can get a free back issue just by asking. Good folks fine magazine.

[Delmonico]

Interesting, but the 303 British round was originally loaded with a solid black powder pellet and a jacketed bullet before they changed to cordite.

Just like the cordite, the loaded it in a unnecked case and then necked it after the charge was in. 

[TAkaho kid]

Interesting, but the 303 British round was originally loaded with a solid black powder pellet and a jacketed bullet before they changed to cordite.

Good point Del,

Note the following:

as originally adopted, consisted of a 215 Gr, round nosed, cupro nickel jacketed bullet with of 71.5 Gr of RFG2 Blackpowder. The powder charge was pressed into a pellet with both ends slightly rounded and pierced with a central flash propagating hole. There was a glazeboard wad on top of the charge to protect the bullet base. It had a small boxer type primer and was officially designated "Cartridge, S.A., Ball, Magazine Rifle, Mark 1.C. Solid Case, .303inch". Muzzle velocity was 1830 fps, chamber pressure about 19 tons per sq".

That "central flash propagation hole" makes all the diffrence. You find a similar configuration with Pyrodex pellets. The hole is for a reason. If that hole didn't exist there would have been many 303's in fragments. 

I also find it interesting that at that early date (1889) they were using a jacketed bullet with the black powder.

They had this to say about the cordite load:

Cordite became the propellant from 1891, the "Cartridge S.A. Ball, Magazine Rifle Cordite Mark 1", had a 215 Gr round nosed cupro-nickel jacketed bullet with a muzzle velocity of about 1970 fps, chamber pressure of about 17.5 tons per sq".

Cordite consisted of 58% Nitro-glycerine, 37% Nitro-cellulose and 5% Mineral Jelly, normally formed into rod, but tubular, tape, flaked and sliced cordite were also used.

[rifle]

The way I understand it a little compression is an assurance that there is no air space between the powder and bullet. What I understand is that people compress powder in an attempt to gain accuracy.I've come to understand that is treating tha symptom and not the cause. The cause being a "not firm enough" crimp.

Blackpowder likes a firm crimp to get a good consistant burn going.Getting a good consistant burn going by compressing the powder is asking for trouble in my opinion.Using a "fine" powder as was used in the Greener is asking for trouble too since the presures rise with the faster burn rate of a finer powder.
Rifles use Fg and FFg better and safer than finer powder. Even the 30-30 would probably benifit from using Fg or FFg in a rifle with the Ballard type rifling.
The 30-30 rifles don't all have a rifling suitable for using black. Some Marlins have the "Micro groove" rifling that would be a waste of time with blackpowder and Marlin does make a rifle with the Ballard rifling ,I think, but I don't know if it is chambered for 30-30. The Winchester has a better rifling for black. I've read about people getting 30-30's to shoot black well but don't remember how. Maybe the use of Fg powder is the trick.

People do compress blackpowder all the time in the 45/70 even with the tapered case. There are compression dies sold for that and they seem popular with the blackpowder cartridge shooters.Some shooters compress a lot more than others and that invites trouble in my opinion. The 1/16th and 1/8th in. compression is the most I compress since I don't like an air space to form in my cases but....more compression than that and especially enough compression to turn the blackpowder into a solid mass makes me nervous. Compression of the blackpowder in the cap&ball revolvers seems to help accuracy but.....they don't have any "crimp". Unless you consider the loading plunger moving lead against the chamber wall. That still isn't firm like a crimp though.

[TAkaho kid]

Rifle,

I wouldn't let this put me off to compression as my religious upbringing tells me: Moderation in all things.

Excessive compression - bad

Air space bad. (For safety we'll leave that as it is. my come back to it another day)

[Delmonico]

Thanks, I had never seen anything about the central hole.

[TAkaho kid]

No problem Del,

It pretty interesting stuff. Imagine black powder driving a 215 grain bullet at 1830 fps  and generating  19 tons of pressure.
What makes it even more interesting is that is only 140 fps less then the cordite load.

In addition the cordite load generated only 17.5 tons.

[Delmonico]

Cordite, is fasinating stuff in it's own right.  It's often written how the big British rounds were underpowered for their case size, but they extracted out of those double guns no matter how high the temps were.  Of course the fact that it was consitant enough lot to lot to regulate a double rifle is also amazing.

[Grapeshot]

I have been reading Spence and pat Wolf's book, "Loading Blak Powder Cartridges for Original .45-70 Springfield Trapdoor Rifle and Carbine."

He indicates that the original loading of 70 Grains of 2Fg was compressed over 0.6 inches for the M1881 500 grain Arsenal bullet.

He also advocates the same be done with todays Goex 2Fg and Winchester Brass after opening up the primer pocket flash hole with a #41 drill bit and use either a Winchester or Federal Large Rifle Magnum Primer.

Having done this myself,  I end up with a solid mass of BP in a .45/70 Winchester case.

This is supposed to be dangerous now?

[TAkaho kid]

Hello Grape Shot,

Not necessarly. The incident thar Greener talked about involved a cheap fine powder. How fine Greener dosen't say. The incident that Bill Knight discribed involved a popular bp-sub that fused into a solid lump under pressure.

There are a lot of variables. For instance the quality of the polishing and glazing of the powder, graphite coating etc.  A well glazed powder will actually give an audible snap when a grain is broken. Poor powder will simply crumble silently. Its far more likely to "fuse" into a solid lumb under pressure.

The question is how far can you compress any powder before there are issues.

Like many thinks having to do with black powder we have to rediscover what "the shooting cranks" learned over centuries of use. This is one of those.