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#577532 08/11/20 09:03 AM
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What is the ballistic difference between Dacron stuffing and backing Rod in loading smokeless for black large caliber cartridges?
Is there any difference?

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They both work great in my opinion. I find that backer rod is the easier of the two to use, especially in the straight walled cases. Just buy a size that is slightly larger than the case size and cut a length about 1/4 inch longer than the air space you have in the case. Stick it in, seat the bullet, and done. With Dacron it's harder to get the same amount measured out so you can have consistency from round to round. I think the backer rod is cleaner on the range as well. The dacron can make kind of a mess.

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Sorry. I missed "ballistic" in your question. I don't notice one. If you were using a slower burning powder than most do however you can compress the Dacron more which might help in that scenario.

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Thank You dearmer
My concern is whether the backing rod seals the charge behind the bullet as well as the Dacron

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I'm assuming you're using lead and worried about gas cutting? I honestly don't know. My guess would be that the Dacron would be better in that regard but the backer rod is so cheap and easy why not just shoot a few groups and see?

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Please excuse my ignorance but what is "backer rod" and where do you get it? I have used dacron for years without an issue.

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WBLDon, you must be lucky. Charlie Dell in his Modern Schuetzen Rifle performed extensive testing on chamber ringing. This ringing had first been noted by the Frenchman who had developed smokeless powder and was reported later by Major Sir Gerrald Burrard in British shotgun chambers. In Dell's testing he found he could ring a chamber at will using dacron holding the powder to the rear of the case. The ring would form gradually at the base of the bullet. Depending on the quality of the barrel steel it might take 6 to 30 shots to form to the point that it was hard to remove the case from the chamber. He also did it using a thin cork wad on the powder. A thin cork wad off the powder by .20 or so did less damage but was still a factor. Kapok seemed to cause less problems than dacron. At one point he even discovered that he could ring the chamber with no filler/wad at all just by shooting straight up. The problem was that a high intensity pressure wave formed on a level surface of powder and propagated to the base of the bullet. The same powder spread out in the case was no problem. A full case of powder was no problem and a case completely filled with something like cream of wheat or corn meal over the powder was also no problem.

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Charlie's experiments were a bit curious. Note that shotgun wads do exactly the same thing as dacron. Same fast powder too.

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I thought the problem could occur if wadding was used over powder, with an air space to the bullet base? The shotgun shell concept may not be the same as using a reduced volume smokeless load for cartridges originally loaded with black powder?

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craig, it may not be the same, but what part of the explanation for Dell's conclusions don't apply to shotguns? The laws of physics, etc. don't change.

I and a few friends have been loading bpcr cartridges with light loads of Unique, 4227, and similar powders, then pushing 3/8" of fine-pore floral foam over the powder until it crushes. This also holds the powder on the primer and creates a sizable amount of space to the lead bullet. Accuracy is greatly improved in most cases. No problems have been reported.

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Brent, I know it is done and will continue to be done. I believe there is no part of a shotshell with a conventional wad that approximates dacron or floral foam over a relatively large air space. Even when shotshells use wadding, there is no load that I am familiar with that has a significant air space that a wad accelerates across before it encounters a stationary shot column. I understand some wads have a crush zone that may be largely air, but that is an engineered control feature not a potential air hammer.

I certainly believe that you have consistent, long term, excellent results with those fast powders, but would you use the same loading technique with 5744 in a BPRC? Though it wasn't mentioned, my suspicion is that the goal is to approximate original ballistics with slower smokeless powders that will not fill the types of cases that are probably being considered. If I had to guess, Unique or 4227 may do for reduced loads, but not likely to approximate traditional full power double rifle loads. But, I'm sure there are exceptions that I'm not aware of.

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Originally Posted By: WBLDon
Please excuse my ignorance but what is "backer rod" and where do you get it? I have used dacron for years without an issue.


Backer rod is used for filling up space you are going to caulk. You can find it at hardware stores in different size diameters.

Ken

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Thank You Ken!

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BPCR?

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Black Powder Cartridge Rifle

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Thank you Rem.,
So, if the use of Dacron can lead to ringing the barrel what about the backing rod?

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A shotgun shell is solidly filled from the powder to the shot like a rifle case full of COW from powder to bullet. It's the powder surface parallel to and spaced from the bullet's base that acts like a shaped charge and a wall of high pressure meets the bullet's base and acts sideways to form the ring. Unfortunately it is more likely to happen in old barrel steels which may be on valuable rifles. I have not found any need to use a filler in any of my large capacity (relative to the amount of powder being used) cases. If you are using any wad on top of the powder and spaced from the bullet please stop at the first sign of a case resisting extraction. The ring will form where the base of the bullet sits and will progressively get worse.

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Found this in a previous discussion:
Major Sir Gerald Burrard in the second edition of The Modern Shotgun (1948), Volume 3, The Gun and The Cartridge, “The Diagnosis of a Burst” discussed “Wave” Pressures and the etiology of multiple bulges pp. 364-375.
p. 365
When the explosive charge was placed entirely at one end of the closed vessel (discussing experiments by Paul Marie Eugène Vieille and published in Etude des Pressions Ondulatoires in 1890) the gases given off naturally rushed forwards along the length of the vessel until the forward layer of gases was suddenly checked by the closed end. When this occurred the gases which were behind the extreme forward layer over-took this layer and began to pile up against it, with the result that the extreme forward layer was compressed with great violence. It was this compression of the extreme forward layer of gases which caused the high pressure…
p. 368
Since this wave pressure acts radially outwards the wall of the barrel is submitted to a very severe pressure all round its circumference, and if the pressure is sufficient to stress the barrel beyond the elastic limit of the steel a permanent bulge all round the bore is the result. Such a bulge is knows as a “Ring Bulge” …

Note that if the surface of the powder is not perpendicular to the run to the bullet then the shaped charge effect is broken up by the random nature of the pressure "walls" formed off the uneven surface. Also note that Dell was able to ring a barrel with no wads at all involved merely by shooting straight up thus starting with a level surface on the powder.

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Justin,

Placing anything in the case CAN result in chamber ringing. It doesn't matter what it is. The problems with Dacron (or anything else) arise when people place a small amount in the case to hold the charge back with airspace between the filler and the bullet. When the powder is ignited the filler is propelled into the stationary bullet which acts like an obstruction and the filler is forced to move outwards causing the ring. If you choose to use filler (and there are situations where you have to) you MUST completely fill the air space in the case with the filler. Doing it this way results in a progressive amount of force being placed on the bullet as the filler moves forward. This eliminates the problem of the filler gaining momentum and then impacting the bullet which causes the ring.

What exactly are you loading for? If you're loading for a single barrel rifle you have more options than if you're loading for a double as you don't need to worry about regulation. Many black powder cartridges can be loaded with 5744 or Trailboss with no filler needed. If you are loading for a double though you may not get it to regulate with those. If loading nitro for black (NFB) loads in a double, IMR or H4198 with filler is a standard loading that's used by many many people (including myself) with no issues in rifles that cost more than most cars to replace if damaged.
If you're loading full nitro loads in a double rifle you can usually use IMR or H4831 without filler. There are exceptions though and the 450 and 475 3 1/2" Nitro come to mind. There is just to much space to get reliable ignition without a filler. Even when you can get away without a filler many choose to use RL15 and a filler as it results in less perceived recoil. This is not something only done by a few, it's common in the world of nitro double rifles. It's the way Kynoch chose to go when they reintroduced nitro express ammunition. They even sold cut up backer rod for others to use in reloading.
The internet is a wonderful place to get info but you need to be wary of where it comes from when everyone has a voice. It's worse when you don't ask a specific enough question and others speculate.

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So, the ringing potential can be mitigated by filling up the cartridge with Dacron,over the powder,to the very top and then inserting the bullet?
Does the backing rod melt away before the pressure hits the bullet thus negating it's taking up all the space between powder and bullet?
Anyways,I'm shooting an old black powder double. Late Victorian age. I use the IMR 4198 powder and a hornaday 300grain bullet.

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Justin,

You may want to read some DGJ articles by Ross Seyfried and Sherman Bell. The articles are great on loading NfB loads. Also, Graeme Wright's book Shooting the British Double Rifle discusses chamber ringing and includes a picture.

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Since most of us are unlikely to run across a copy of Wright's book, do you suppose you could give us a quick rundown of what he wrote about chamber ringing? Please?

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KDGJ
I can’t recall Seyfried or Bell discussing chamber ring bulges. If you have a specific article in mind,please let me know.

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DGJ 2011 summer Bell has a great article on fillers.

https://www.castbulletengineering.com.au/downloads?download=9:finding-out-for-myself-express-rifle-case-fillers-by-sherman-bell-thanks-to-the-dgj


http://www.bertramandco.com/

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Justin,

Seyfried briefly touches on chamber ringing in Vol 10, Issue 4. His articles in Vol 5, Issue 4 and Vol 6, Issue 1 provide his techniques/approach for loading NfB loads. As Steve mentioned, Bell did an extensive set of articles on Finding Out for Myself with specifics on NfB loads. These can be found in Vol 15, Issue 1; Vol 15, Issue 4; Vol 16, Issue 1; Vol 19, Issue 3; and Vol 22; Issue 2 (Express Rifle Case Fillers). The issue looks at pressure spikes with the different fillers.

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Sherman Bell's testing was very interesting and covered the gamut of filler material. He said he was surprised that the closed cell foam which he knew of to have caused 2 instances of chamber ringing did not show any reason in his test to have done so. What he did not test was any powder except 4198. He did not mention if the two instances of ringing involved 4198 or some other powder or if those instances were in older barrels which he admitted may be at more risk than the modern barrel material he was using. I would be mindful of the tests that produced "stepping" of the pressure curves as the more likely problem makers under slightly different conditions.

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Originally Posted By: HalfaDouble
Since most of us are unlikely to run across a copy of Wright's book, do you suppose you could give us a quick rundown of what he wrote about chamber ringing? Please?


He believes it is a result of airspace within the load. The airspace allows for a pressure wave to be created. The theory is based on Paul Vieille's (1890) theory of "Wave" pressure. Burrard in The Modern Shotgun (1948) summarized Vieille's theory to explain what happens inside a cartridge case. Vieille proved that the high end pressures were caused by the movement of the hot and very elastic powder gases When the powder is ignited at one end, a wave of high speed gases accelerated through the airspace. As the wave hit the solid end it stopped, and as the following gases piled up behind, the forward layers were compressed violently causing a localized area of high pressure.

(You already mentioned this book by Dell and it is in Wright's write-up on Chamber Ringing): Charles Dell co-wrote The Modern Schuetzen Rifle (2nd Edition 1999) with Wayne Schwartz. Charles Dell was able to backup Vieille"s theory. That is, chamber ringing is caused by high velocity gases hitting the base of a stationary bullet. This creates a very thin, but high pressure gas area at the bullet base, and when this exeeds the yield strength of the chamber steel, a ringe is formed.

Ken

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Thank you SKB and KDGJ. I will get on these articles ASAP.

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Anybody really interested in this discussion should actually read the Bell article( SKB above showed a link to the article) in detail, especially the conclusions and the pressure curves/chart. His testing of 15 ,different materials/methods failed to show any significant spike in pressure. Regarding the "stepping" or "stuttering", a study of the pressure curve shows that the pressure actually dropped( likely when the bullet started moving, chamber volume increased, slightly lowering pressure until it "caught up"), but never showed enough pressure to ring a chamber. In his conclusion he stated " The obvious elephant in the room is that no excess pressure developed from the use of these widely different filler material". One of the most "telling" results was the showing that the system currently used by Kynoch produces some of the highest pressures, and they are still not excessive. I will continue to use a "tuft" of kapok tamped down on the powder, as I have for half a century; but I will be responsible, myself, if anything happens. I have never seen a "ringed" chamber but enough other people talk about them that there must be some basis. Maybe someone that has a rifle with such a chamber will closely examine it for significant prior use with shorter cases. This may create a "ring" by erosion and if a new owner starts loading proper length cases( much easier to find now than years ago), it may take a few reloadings of new thicker cases to expand into "old" chamber rings, causing extraction problems. This is just a thought, not a proven fact.
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Mike, Charlie Dell started with a fresh cut chamber and the ring formed at the position of the base of the bullet.

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HalfaDouble,
I didn't read Dell's report, did he provide pressure curves, or did he measure pressures? Smokeless powder is not an explosive, it is a flammable solid. It must burn enough to create enough gas to build the pressure that increases the burn rate( speed). Granted, this occurs in a very short time, but it is very difficult to imagine a sudden "wall" of high pressure gas hitting the base of the bullet and moving sideways, while the rest of the vessel( cartridge case) is at a different pressure. I know my training is construction, not fluids, but it would be easier to understand if there were pressure measurements showing pressure exceeding the elastic limit of steel. BTW has anyone reported bulges at the location of the "rings" or is the steel compressed? Note: this is not a smart a$$ question, I'm interested.
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No, he just shot it until a ring formed. Might have taken 5 shots or 30. Then he reset the barrel and rechambered it and tried a different test. Some of Bell's tests did show a higher pressure at the bullet's base than, what was it, an inch below that. It's not an abnormally high pressure load that does the ringing but the result of the directed pressure wall hitting the bullets base and exerting its concentrated force sideways. It's like a shaped charge effect - https://en.wikipedia.org/wiki/Shaped_charge

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HalfaDouble,
I am somewhat familiar with shaped charges, having completed basic class and practical training in demolitions with the US Army Corps of engineers, which is nowhere near as extensive as my friends in EOD (Explosive Ordnance Disposal). The reasons I am unsure that a "shaped charge effect", rather than something else caused the ringing are: a shaped charge requires a high explosive( smokeless powder is a flammable solid); the charge( explosive) itself is shaped with a void( generally cone shaped); the effect is linear( along the axis of the void); for a "shaped charge effect" to produce the pressure to dent the steel, it should leave some signs on the brass case, if not cut it through. While I have never seen "ringing" happen, enough people have, that I can believe something causes it. It seems, therefore, that if the actual cause can be determined, it can be avoided to avoid "ringing" while gaining the advantages of fillers. This would require much more research than I am able to do. It is known that Kynoch uses foam filler in their NIB loads intended for old rifles, so they must have done extensive research into fillers, maybe you can obtain a copy and share it here.
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The use of fillers, tests and their results is always interesting to me. I've read all of Bell's and Seyfried's articles and distinctly recall that in a subsequent issue Bell specifically warned against the use of closed cell foam fillers. Unfortunately I don't recall if he mentioned a reason other than what he thought was too high a pressure....which seems enough not to use them.

The "stutter step" Bell mentions is curious but, as Mike observed, the pressure does not increase to the level it would ring a chamber.

As with Mike I've used fillers for....well, a long time, decades. Right after reading Wrights book on doubles I eschewed granular fillers such as COW and resorted exclusively to open cell foam fillers. If memory serves, they were 3rd on Bells list. His first choice was cotton balls, then Dacron then open cell foam. I've never tried backer rod but suspect open cell foam acts much the same. J.C. Munnel has used Styrofoam packing peanuts for quite a while and from his writings no problems have developed.

That fillers are controversial goes without saying. However, as with Mike I've never seen a chambered ringed because of their use. Also, as with Mike, that it happens cannot be denied. I have old, German rifles that have fired hundreds of rounds of cartridges loaded with an open cell foam filler over Unique, Reloder 7, IMR-4227, IMR-4198 and 4895 and H-4895 and have yet to ring a chamber. Maybe I've been lucky and might ring one today if I shoot one of those rifles and loads. However, given past experience it seems highly unlikely.

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I'm not sure why I posted here. I knew better, but did it anyway and now I kinda feel like I need to justify/explain some of what I said. I originally responded to Justins question with the assumption that he was already loading NFB rounds with Dacron filler and knew the potential hazards involved. Therefore my statements were made with that in mind. I also used the word 'must" in one of my posts which we all know is not true. I used it in the same way as I would when telling someone that they must look both ways before crossing the street. They certainly don't have to, but it would be foolish not to.

With that out of the way I work in the explosives field and have for my entire adult life. I manufacture, test, and dispose of explosives for a living. I've been lucky enough to have a very diverse career that has allowed me to work for several different companies and agencies giving me a much more rounded knowledge base than many others. I don't know everything but I when I speak to these things I do so with a lot of experience and education to back it up. I also load for a lot of guns, including doubles, both with and without fillers.

I'm going to try and write a few things here to hopefully shed a little light on things for some people. I'm going to write this as a forum post though, not as if I'm writing a peer reviewed paper for a scientific journal. Things will be (sometimes) overly simplified to make things easier to understand and to save me time. I'm writing this to try and help others not to help myself. If people have serious questions I'll try to answer them if I have time. If people want to argue I'm gone.

Many people are referencing studies that only looked at one variable and then intermix these studies trying to come to the conclusion they want to. This is a large part of the problem. Vieille and Dell say they can ring a chamber with just powder yet Bell couldn't. Why not? The answer is that the powders used were very different. Explosives are generally rated by "power" and "brisance." For this discussion power will be the total amount of gas created by the explosive. So if 10 grains of powder X creates 1 cubic foot of gas it's twice as powerful as powder Y that creates .5 cubic feet of gas with the same 10 grains. Brisance is the speed at which those gasses are created. They are both important but do different things. 10 pounds of black powder will be more powerful than 1 pound of RDX. If I place these two explosives on a 1 inch steel plate the larger charge of BP will just bend the plate while the smaller RDX charge will blow a hole through it. The brisance is what cuts through the steel. With smokeless powder the basic makeup is more or less the same and therefore the power is very close to the same for the powders reloaders use. Additives are added to slow the powder down and lessen it's brisance and this (along with grain shape) is what changes where they fall on the burn rate chart. A case full of Bullseye doesn't necessarily have more power than the same case full of 4831 but the brisance is totally different. This causes the pressure to spike more quickly with the bullseye to where things fail even thought the total energy (power) is the same.
So...if you use a faster powder you are more likely to ring a chamber as the brisance is higher and it creates a stronger shock wave (which doesn't necessarily correlate with pressure) which can ring a chamber as Vieille found out. When an explosive detonates it creates a large cloud of gas which radiates outwards. The leading edge of this cloud is where the shock wave lives and it's what shatters things it comes in contact with. It can bounce off things and it can compress things (including air). Since the shockwave radiates out from the explosive, if a case is pointed up, the wave will radiate towards the bullet since all the powder is at the base. This will cause a convex wave to move towards the bullet (which is an obstruction) until the wave hits it. The whole time it will be compressing the air in the case (since gas is compressible). When the top of the wave hits the bullet in a straight walled case you will have all the compressed air (and a portion of the shock wave) forced into the bullet case junction by the shock wave. Remember it's convex shaped so it will be forcing everything into this area as it moves forward. This is why the ring forms where it does. If the powder is laying on it's side when the cartridge is fired the wave will form differently and start at the base of the charge and move forward and sideways from it and will impact the bullet in a very different way. This would explain why chamber ringing wasn't seen when the charge was fired in this way.
So what can we do about it? Use slower powder. When you use slower powder we generally use more which has less brisance and fills more of the case so we have less air space. Two birds with one stone. We all know that at a certain point it's too slow to reliably burn though so we either need to go back to a faster powder, shorten the case, or add something to fill up the space in the case and/or hold it against the primer so the powder can stay in contact with it long enough for the flame front to encompass it.
Placing a small amount of something over a charge of fast powder probably makes things worse as it holds the charge against the primer longer allowing the flame front to travel quickly. This causes the shock wave to form perfectly at the furthest end of the case and ensures all the powder burns. I myself would not do this although I know some people do and haven't had issues. As you move to a slower powder the risk of doing it this way is reduced and you can get a cleaner burn with more consistency. I still personally choose not to do it this way.
There's also another thing we need to look at when we introduce fillers. Just as the bullet is an obstruction to the shock wave it's also an obstruction to the filler which will be propelled into the stationary bullet at extreme speed. This can also ring a chamber in the same way as an obstruction in a barrel creates a bulge when you shoot a bullet into it. The problem is how do you determine which one is doing it and how much one contributes to the other? This is not something you can figure out with 100 tests. It would be much more involved and very expensive. Some fillers are frangible and break up (likely by the action of the primer) and may not cause as much harm as another that is solid. I can speculate but NO ONE can tell you for sure without a lot of testing. One thing I can tell you is FILLING the case with filler (when you choose to use one) has advantages. First it will take up space. You're substituting a solid for the air in the case. The more you put in there the less air. The second benefit is that if you put in enough filler that it is touching the bullet base as the charge pushes it forward pressure is progressively raised until the bullet starts moving. We all know throwing a baseball hurts less than slapping one. This is how I choose to use fillers knowing what I know.
This is just the basics. There is so much more that influences this discussion. Different grain sizes and shapes will be easier to ignite than others. The primer will disperse some powders through the case in different ways than others prior to full burn. This will effect things. Bottleneck cases will redirect the shock wave differently than a straight walled case and will also compress the filler more in this area. This will change things.
In the end there's only a few things anyone can tell you for sure:
You can ring a chamber with powder alone.
You can ring a chamber using fillers.
You can load with just powder and not ring a chamber.
You can load with fillers and not ring a chamber.

I hope this helps some people understand how things work and explains why you don't have the powder companies giving you the magic formula to alleviate this in all circumstances.

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I don't think your thoughts should be assumed to be unappreciated. Another point that you could consider that is mentioned in most reloading manuals is that some slow powders burn erratically when attempts are made to use them at a lower pressure than designed.

I suspect ringed chambers are as you say, somewhat unpredictable, likely not very prevalent, but apparently a pressure spike or localized pressure spike. I have all the mentioned references, just not quite the time to dig into them for curiosity and to see how they might relate to ringed chambers. A common theme though seems to be relatively high volume cases, with the intention to load to relatively low pressures?

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Dearmer, great post and thanks very much.

I would like to send you a PM with a question or two, if you dont mind.

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dearmer,
Thanks for the effort, it is obvious you put a lot of effort into the explanation. I guess you are saying "it just depends", and it depends on unknown variables. I guess some of us accidently found a set of variables that work and others found a set that didn't. It would be nice to have a way to measure the pressures resulting from a particular set of variables. When pressure was measured with copper/lead crushers, the results only( or mainly) showed maximum pressure. I had hoped Bell's use of more modern equipment would be the answer, after all, he was able to show the "Stutter", therefore should have shown any "spike" also. Do you think measuring Dell's loads using Bell's methods would result in a showing of a "spike", sufficient to cause a "ring"( maybe with multible "shots") and the amount of pressure necessary to do it? Instead of being similar to a "shaped charge", your explanation sounds more like a "water hammer" resulting from quick acting valves in a plumbing system, except water is not compressable and gas/air is. A common "fix" to stop water hammer is a column of air trapped in the system( like above the powder in a cartridge) to act as a spring. It's a "puzzlement".
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I'm glad some people are finding this useful. It is certainly difficult writing this in a way I think people can easily understand. One thing I'm noticing is that people seem to be getting hung up on pressure. Pressure certainly matters but the shock wave is different than just max pressure. I've been trying to think of a good way to explain it but I'm not having much luck coming up with a really good way to do so.
A strong shock wave may be 10 atmospheres. That's only 147 PSI but it can shatter concrete, cut through steel, and liquefy human organs. It behaves differently than pressure. It's the rate (speed) of change that matters more than the overall pressure.

Here's a line out of an explanation from Encyclopedia Britannica, "Shock waves alter the mechanical, electrical, and thermal properties of solids and, thus, can be used to study the equation of state"


Does anyone have a complete English version of Vieille's paper?

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I can appreciate that you are distinguishing a shock wave from pressure, it still does appear that the phenomenon tends to happen in large cases loaded to relatively low pressures.

The question would be, why doesn't this condition happen in what are commonly known to be high pressure cartridges. Automatic and semi automatic actions would seem to be dangerously vulnerable to feed and extraction problems, but it doesn't seem to happen?

As an aside, while the dicussion is about ringed chambers, I would think it also relates to some blowups.

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Originally Posted By: craigd
I can appreciate that you are distinguishing a shock wave from pressure, it still does appear that the phenomenon tends to happen in large cases loaded to relatively low pressures.


I would change this to read, it still does appear that the phenomenon tends to happen in large cases loaded to relatively low pressures when less than ideal propellants and questionable loading practices are used.

...and before jumping all over me, this is not aimed at anyone, I include myself in that category. I don't think you'll find a powder company or loading manual publisher that would consider stuffing a varying amount of Dacron, foam, cream of wheat, or dryer lint in a cartridge as a recognized loading practice. We don't do it because we want to, we do it because we need to if we want to duplicate original black powder ballistics in many cartridges that weren’t designed for smokeless powder. The proper powder to use to achieve factory ballistics would be black powder. There's a reason you see powders with names like 50BMG and CFE223. They were designed to have the ideal density and burn rate to work in those cartridges. We don't have a smokeless propellant that mimics the density and burn rate of black powder in all situations so we have to make do with what we have and with that comes risk.

Originally Posted By: craigd
The question would be, why doesn't this condition happen in what are commonly known to be high pressure cartridges. Automatic and semi automatic actions would seem to be dangerously vulnerable to feed and extraction problems, but it doesn't seem to happen?


If we look at modern rounds like the 308 and 223/5.56 they were designed to work with smokeless powder. Their target velocity is achieved with powders that fill the case and work at target pressures. If we were to neck down a 300 Ultra Mag to 22 and try to mimic 223 ballistics we'd run into the same problem. There just isn't a powder that will allow us to easily achieve that without risk.


Originally Posted By: craigd
As an aside, while the dicussion is about ringed chambers, I would think it also relates to some blowups.


Kinda, sorta, maybe???
Again I will do my best to oversimplify this. Please don't jump on me if things are not totally accurate. Excepting obstructions, blowups are generally going to be a result of using too much powder. This will be more common when fast powders are used as less is needed to reach high pressures. In some cartridges two or even three times the max charge can be placed into the case. This is less of an issue with slower powders as more is needed to reach the same pressure and you often run out of space before you can reach a pressure high enough to blow up an action. That said this will apply more to the individual that uses Red Dot in a 30-06 rather than the individual that goes two grains over max with a charge of Varget. The latter is certainly bad but is less likely to result in a blowup.
Smokeless powders are engineered. There’s single base and double base. There’s flake, ball and extruded. Some grains have holes in them others don’t. Some grains are bigger than others. All this is done to modify the density and the burn rate to allow it to perform optimally in a cartridge (or several cartridges). This engineering is almost always done to slow the burn rate. Fast is easier to achieve.
Why do we care about burn rate? As I mentioned before it’s not just the pressure we care about it’s how fast the pressure is created as well.
If I place a car in neutral on flat ground and run into it at 10 fps with my 200 pound body weight I will exert 311 pounds of force on the car. If I assume my arm weight 10 pounds and I slap the car with it at 50 fps I will exert 389 pounds of force on the car. Which one will move the car further? Which one will hurt more? I hope most will agree (otherwise my example sucks) that the first despite being less energy will move the car further and hurt less. Again it’s not just the total energy it’s how and when the energy is released. Another example is in mining. Let’s assume we are quarrying granite and long bore holes are drilled in the rock. If those holes are filled with a slow explosive the granite will separate in large chunks. If a fast explosive is used you will get stone dust. The total pressures can be made to be the same but the results will be different. This hopefully helps you to understand why we choose one powder over another.
If we use a very fast powder in a cartridge it is possible to raise the pressure so fast that the action fails before the bullet can be expelled. That’s the reason we can’t use high explosives in guns. In a perfect world the propellant would start burning slowly until the bullet began to move and then rise to max operating pressure and stay there until the bullet just leaves the barrel where it would be totally consumed. Unfortunately they don’t work this way. They usually work just the opposite and reach peak pressure quite rapidly and then drop off as the powder burns and as the internal volume increases (due to more barrel length being available as the bullet moves forward). The powder manufactures try to make a powder that will fill the case and slowly and over time push the bullet forward so the chamber pressure stays in the target range without going over. So why don’t we just use slow powders for everything? A byproduct of modifying/slowing the burn rate is that those powders require higher pressures to fully combust. If the case volume is too big and the projectile too light the powder will not burn completely (if at all) and you often get a bullet stuck in your barrel. In many pistol cartridges the pressures needed to ensure a good burn with slower propellants are higher than the pistol can withstand so you need to go to a faster powder to get it to burn at the lower pressures. This is why there are so many different powders and why not all work in every situation (cartridge). This is why high volume cases (usually originally designed for black powder) require faster powders and have more room in the case than needed. This room allows for the potential of double charging (with a powder that’s less forgiving) and these fast powders and air space can also lead to the chamber ringing. I guess they are related in that way but the reasons they happen are different and the mechanisms that create them are different.

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Originally Posted By: dearmer
....Which one will hurt more? I hope most will agree (otherwise my example sucks) that the first despite being less energy will move the car further and hurt less....

Ah, but there in lies the rub, on the arm that is. Does the arm move the car less because some of the energy was expended to create the hurt, not movement?

Just kidding. Hey dearmer, thanks for taking so much of your time to lay your explanation.

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dearmer,
Just for information, slow powders in rifles can cause blowups. A famous example is the case of 270 Win. loaded with less than the recommended amount of 4831. This is another one I have never seen but has been reported enough that it must have happened. Enough cautions have been given about this that instructions for loading 5.6X61 vom Hofe S.e. make particular mention of it. Also One of the Engineer BNs I was in ran a quarry for training. Military Dynamite was used in blasting( fairly slow) with good success, but when the ran out and used some C4 (much faster)they didn't get dust, the got chunks as large as house trailers, whish had to be blasted again to get them small enough to fit into the crusher. The Dynamite would "heave" it, but the C4 would "shatter" it along fault lines. I don't know if this affects your examples or not.
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Originally Posted By: Der Ami
dearmer,
Just for information, slow powders in rifles can cause blowups. A famous example is the case of 270 Win. loaded with less than the recommended amount of 4831. This is another one I have never seen but has been reported enough that it must have happened. Enough cautions have been given about this that instructions for loading 5.6X61 vom Hofe S.e. make particular mention of it. Also One of the Engineer BNs I was in ran a quarry for training. Military Dynamite was used in blasting( fairly slow) with good success, but when the ran out and used some C4 (much faster)they didn't get dust, the got chunks as large as house trailers, whish had to be blasted again to get them small enough to fit into the crusher. The Dynamite would "heave" it, but the C4 would "shatter" it along fault lines. I don't know if this affects your examples or not.
Mike


I would never be so bold as to say it's impossible but I have more faith in peoples ability to lie after an accident than I do in the ability of a reduced charge of 4831 to blow up a 270. I was just reading about this a few months ago on another forum where someone had an accident and everyone was talking about how this can happen. A week later the individual admitted that he had accidentally loaded the rounds with the wrong powder. He grabbed a can with the same color label and thought if was the correct powder. I believe he is in the minority that either realize they made a mistake or admit to it.
I have never seen a real study that was able to reproduce this. If someone has and can send me a copy I'd be happy to take a look at it.

Your quarrying example makes sense. Like I said, my examples were oversimplifications. Lots of things come into play. The fact that you stated it "shattered" along the fault lines is what I was alluding to. Things will usually break along the weakest part. If that fault was not there it would behave differently. The old pineapple grenades break into large chunks because deep cuts are cast into them. Without them they would break into smaller more random pieces.

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dearmer,
I can agree with your faith in the ability of people to cover up for an accident; but when I had to reduce the speed of lightly constructed 22 HP bullets in my 5.6X61R vom Hofe to 3000 fps, so it would group, I still changed from 4350 to 4895 rather than endanger an heirloom rifle.
It's possible some with ringed chambers could have this same ability; consequently my interest in the real cause and conditions, if any, for chamber "ringing". The point of the C4 story was " lesser" explosive worked while the High explosive didn't. It was OK though, the purpose of the quarry was for training( even though we did use the rock, training other troops) and that provided a good lesson.
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dearmer, thank you for taking the time to post your educated views. Too often we hear about something fourth hand or a reasonable ( on some level) story is repeated to the point it is taken as gospel.

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