For awhile now I have always thought the standard 80% from full load density was the lower limit because of the possibilty of detonation caused by to much air in the case. In other words if the load density for a case is 54 grains then the loads should not go below 43.2 grains or 80% of 54. And they should not go above 86% or in this case 46.44. But then how is it that Herc 2400 can be loaded in .308 cases at 24-25 grains without detonation taking place? Has anyone tried 2400 in a 30-06 under the 80% load density?

This is an area of internal ballistics that should be really addressed by the powder manufacturers. If you look at loads from Winchester for their 296 powder there are usually very blunt warnings about not using reduced loads. Yet other powders are very suited to reduced load use and some are specifically designed for it. I personally would not follow a generalized rule about what load density is safe. I would ask the manufacturer about each specific powder and the load I intended to use. Smokeless powder's burn characteristics are significantly affected by the containment factor as I like to call it. Technically not accurate, but you might get the idea. Don't assume anything about the safety of a "light" load - ask the manufacturer.

You might see the phenonenom you refer to in a shell case for a 105 howitzer or similar, but in a rifle case????? Been LOTS of research and disscussion on this for years. Labs have never been able to prove the existance of such a thing in a rifle case.I wouldn't go sticking a 20 percent charge of 760 or other ball powder in a 300 win mag case and popping it off, but 2400 was developed as a fast RIFLE powder, it has been used from its inception as a reduced power powder. Too many people for too many years have used pistol/shotgun powders like Unique for very reduced velocity loads to call the practice unsafe. Untill recently,(the 48th Edition) Lyman published tons of data using such powders and cast bullets in rifle cases.

The problems come about when folks start trying to get full velocity from too fast a powder. Witness the recent threads about the use of Blue Dot in 223. Seems that someone decided to try and duplicate full velocities with the stuff. Apparently there was a lack of understanding as to what makes a fast powder fast. It ain't about velocity. It is how quickly a powder develops pressure. The faster a powder makes pressure, generally the lower the velocity we can expect from it in a given application, as it develops full pressure without making enough gas to reach full velocity.

Stay with published data. Go to gun shows and yard sales and buy evey older manual you can get your hands on, especially those of Lyman. I'd be more than sure such data is available in the 3rd edition of Lymans Cast Bullet Handbook. Most of these loads could be used with a jacketed bullet, use caution and stay above 900 fps, and don't exceed listed maximum charges.

I have heard that "detonation" is only a concern in larger cases and only with slow powders. The limit you refer to (80%)is interesting, so I looked it up, by checking what my manuals had of loaddensities for a 416Rigby (which is a large case using slow powders and the one that I am corcerned about regarding "detonation) Checking under Vithav. 165 there is a range from 77.2 to 96.6grains. 77,2 is exactly 80%loaddensity in this case.
Checking same caliber for H4350 there is a range from 63.9 to 90.5 Here 63.9 is below the 80% loaddensity... I don't know much about "detonation" I don't think anyone really does, but it seems like your 80% limit is fine to go with and it is backed up by published data. (Hornady reloaders manual #5)

Detonation refers to an explosion that results in shock waves being propogated faster than the speed of sound. That happens every time you fire a CF rifle. I guess the safey concern with cartridges filled with fast burning powder and too much void space is that the air, when rapidly heated, will result in enough pressure when added to that generated by the hot gases of combusion to exceed safe limits. Or maybe that too much pressure can build too quickly before the bullet begins to move.
The surest way to blow up a barrel of a muzzleloading rifle is to "short charge" it, in other words to leave a pocket of air between the powder and the projectile.

I read a great article on it. The article stated the US Army has known about detonation for years. The Army knows what makes it happen according to the article. It seems to happen when the flash from the primer can ignite both ends of the powder column at the same time. This can only happen when the full length of the powder column is below the flash hole. I can't say this info is accurate but seems logical.

I have a stack of reloading books from a bunch of the major bullet manufactors and have used thier data as a guide to start. I have always found my most accruate load somewhere in between thier low and high figures. But I was reading about detonation and how the small loads will ignite so fast it can cause quite a bang and raise pressure quick. I am not working on any low loads or anything just wondering about it.

I believe it is a mis-statement that detonation has never been replicated. The Norma lab, IIRC, was able to replicate it consistently.

I believe detonation can only occur when a primer does not do a good job igniting the powder. By heating the powder up, and/or burning off the deterrent coatings, the characteristics of the powder change, and the detonation can occur.

A scenario: A lightly charged 30-06 cartridge is fired. The primer flashes over the top of the powder, heating it and barely starts a burn. Normally pressure would build rapidly, containing the burn. In this case, though, the primer also dislodges the bullet, and sends it into the throat. This increases the effective case size substantially, and lowers the pressure. The lower pressure prevents the burn from building normally, but the powder does heat rapidly. The bullet stops, and now acts as a bore obstruction, just as the powder does take off.

I'm willing to bet a steak dinner that you could produce the phenomenon with any long throated '06 with little neck tension, a heavy bullet, and a 30% charge of slow ball powder, positioned so it doesn't cover the flash hole. JMO, Dutch.

Dutch, wouldn't what you are describing be better called a (very short) hangfire? Your timeline of events sounds logical enough though...

quote:

Originally posted by Blob1:
For awhile now I have always thought the standard 80% from full load density was the lower limit because of the possibilty of detonation caused by to much air in the case. In other words if the load density for a case is 54 grains then the loads should not go below 43.2 grains or 80% of 54. And they should not go above 86% or in this case 46.44. But then how is it that Herc 2400 can be loaded in .308 cases at 24-25 grains without detonation taking place? Has anyone tried 2400 in a 30-06 under the 80% load density?

Why, certainly!! The rules you quote only apply to VERY SLOW POWDERS IN HUGELY OVERBORE CASES!!

Detonations have occurred in cartridges using reduced loads. They usually occur in overbore capacity, small-bore/large volume cases like the .240 Gibbs, .257 Weatherby, etc., when these are loaded with small charges of very slow powders, usually ball powders with a nitrogylcerine content.

No-one has ever been able to produce such detonations "on demand" in a laboratory in order to study the phenomenon, and thus, no-one really knows what causes it to happen. There are a lot of theories as to why it happens, (and they are just that - theories!!) BUT the volume of air in a case may or may not, be part of the cause. These events do not seem to happen with reduced charges of fast or medium-speed powders. For example, cast-bullet loading data has included use of very small charges of powders like Unique, 2400, RE7, etc., and similar powders, ever since people started using smokeless powder. I have never heard of the detonation phenomenon being associated with such loads.

I have detonated 2 grain charges of Bullseye in 357 cases loaded with 148 grain WC bullets. The primers pierced and the cases looked pristine, like they just left the tumbler. The report was very high pitched, almost piercing. Heavier charges of Bullseye fired normally, with sooted cases, normal looking primers, and a completely different report.

I believe that too much primer for too little powder and a lot of empty space is a bad combination.

quote:

Originally posted by CDH:
Dutch, wouldn't what you are describing be better called a (very short) hangfire?

I suppose that's correct. Or a hang-kaboom..... FWIW, Dutch.

For your general information, here are some DOD definitions:

Explosion: Generic term for something going "boom"

Deflagration: Describes a BURNING of powder or solid grain of 3000-4000 feet/sec. It can be a bullet or rocket motor grain, dynamite, black powder, etc.

Detonation: Describes the high velocity explosion with velocity of 30,000-40,000 feet/sec. It is seen with Class A warhead material or other hgh explosive like Symtex or C-4.

I don't know if the "detonation" in some bullets is a true detonation or not. If it is, you can imagine what pressures are involved.

From G Mushial-To use a filler or not, has to do with what it is one is trying to do...There are two methods by which a powder charge can initially be ignited: convective and conductive.

In conductive ignition, after the grains directly bathed in the primer gases have been started, until the amount of available heat is such to convectively ignite the rest of the charge, the heat transfer is from grain to grain via physical contact - hence the term conductive ignition. Because of the nonrepeatability of the packing of the grains, over 10 shots, a good SD (of velocity) will be in the 15-30fps range.

In convective ignition, the heat available from the primer discharge and the resulting distribution of the grains results in each grain being bathed in the primer gases, the surface temperature of each grain is brought up to the kindling point, and as a result, all are ignited within a few microseconds of each other (ie, the leading edge of the time-pressure curve is VERY steep). Because all the grains are ignited in parallel, it is not unusual for SD's over 10 shots to be in the 3-5 fps range [the smallest we've seen is 0.7fps]. Repeatability is only limited by the uniformity of the individual powder grains.

Then the obvious question is: why doesn't one always use convective ignition? The simple answer: convective ignition require specific conditions - a) the powder grains must be allowed to "free float" within the case - they must be uniformly bathed in the primer gases - this will not happen if they are packed or stuck in a corner of the case (or a filler is used); b) there must be enough heat for long enough for the surface of each grain to come up to its kindling temperature - this means not too many grains (actually thermal mass) and not too much volume to distribute the primer heat over; and c) a powder which is friendly to such ignition, ie, not too heavily coated.

In practical terms: this means small, light grained pistol or shotgun powders (with sufficient "sail area" to "float in the primer gases"); and charges less than 18 grains (+/-).

Powders with rough surfaces are better at this than smooth grains - actually a question of thermal mass to surface area ratio. How much is heat required to ignite a grain is determined by its thermal mass; how fast one can impart that heat is determined by the surface area. High surface area to thermal mass grains will ignite more easily than conversely.

The size of the case (read: amount of cold brass/chamber sucking heat out of the system) is a limiting factor in how much heat is available to heat the charge; likewise the volume of the case limits the charge that can be convectively ignited. In a large case, the surface area to cool the gases is increases; likewise simply the heat (energy) per unit volume is decreased.

In practical terms: a 32ws case with small surface area and small volume, the available heat can convectively ignite 20ish grains of nominal powder (*); by the time one gets to a 45-70 size case, that limit is reduced to 16-18 grains; in a 300 rum/458 Lott size case, with nominal powders that becomes 15ish grains (though through careful powder selection can be raised to 16-17 grains).(*) this may not be strictly correct in that given the size of the case, the charge will probaly not be able to "free float" (ratio of volume of charge to case volume is too small) - in a 32ws case useful charges run in the 4-10gr ranges.

One can observe the failure of convective ignition. We saw this in our 300 rum data. At the lighter loads, the heat available provided good clean convective ignition; but with particular powders (read: slower heavily coated, eg, bluedot 2400 etc), as the load was increased, one would see a drop in velocity (by as much as 25%) and it was only after one increased the charge by 4 or 5 grains would one get back to the velocity previously seen. Below this critical charge mass one would see small SD's, in the interim area, the SD/ES's would become huge; and above, they'd settle into standard values for conductive ignition. If one is using convective ignition, one should never intentionally operating in this interim area.

-----------------------------------------
Of note: when CONDUCTIVE ignition becomes CONVECTIVE, that is called DETONATION.
-----------------------------------------

Conductive ignition and loads designed for such rely on the propagation delay to keep the time-pressure curve in check. Convective ignition by design has a very steep leading edge t-p curve. A classic case of detonation is: a rifle case, with a 60% charge, where the charge has uniformly settled, ie, 50% of the charge is below the primer-bullet axis of the case and 10% is above, where when the primer discharges, the 10% above is lifted into the free space above the 50% of the charge, the grains of that 10% are bathed in the primer gases, and instead of ignition over time, are all spontaneously ignited, generating sufficient heat/gas to ignite the rest of the charge, and because of its position, ignites as a shaped charge, and blows the top off of the receiver.

We've been working with convective ignition for the last 9 years now, and especially for target shooting we find that it give us a significant advantage. (But this is not to say that where convective ignition can not be uniformly achieved, we don't revert to standard conductive ignition). UNQUOTE--

Interesting to say the least.Some powder and
bullet and case combinations are dangerous
with convective ignition, that started out as
conduction ignition---Ed.

Very interesting, indeed, though I am a little sceptical about the 60% number.

The reason is that primer explosions are very violent, and usually shatter the powder kernels right in front of the flash hole. McPherson refers to this as "super ignition". It essentially turns heavyly coated, slow burning kernels into powdered, very fast burning propellant. In almost all cartridges, this is what starts building the heat (pressure) inside the case, and helps ingnite the rest of the charge.

The "super ignition" of a portion of the powder, and the associated gradual build up of powder (and starting the movement of the bullet) is the "normal" progression. Powder should be packed in front of that primer.

What is interesting is trying to tie this SEE into the secondary pressure spike phenomenon that Popenmann has recently presented. A "unifying theory" is waiting to be developed.... FWIW, Dutch.

Well that tells me what I wanted to know! Better to stick with good known powder loads than to experment on the outside of the envelope unless you know what you are doing!

Some powders, notably AA 5744, are designed for very low load densities and can't detonate. 5744 has no coating and a good dose of nitroG so it is very easy to ignite and is "self-sustaining"...meaning that the burn rate is not sensitive to pressure.

Dutch--I don't think that what popemann
recorded on secondary pressure spikes is like
detonation.Ie, his problem is ignition slows,
bullet slows and then ignition takes off thus causing a spike.Oh his spikes may cause damage.

In detonation powder starts too fast(6-10 times its normal speed as a propellent), with too much powder, and bullet can't move out, and accelerate down the barrel
that fast, thus acting as an obstruction, and then guns come unglued...Ed.

A detonation is where a shock wave moves through the explosive and causes a decompositon of the material. The shock wave is self sustaining and is in the neighborhood of 2000 to 8000 meters per second. During the detonation large amounts of heat and gas are generated.

All explosives have a shock value that will cause them to detonate. No heat involved. The is also a heat value that will cause them to detonate (I think true of all explosives). Heat, pressure, and shock in combination can complicate the conditions.

Detonators are primary explosives that are usually set off by heat, but shock can do it also. The detonators are used to set off secondary explosives like C4, TNT, etc. Ammonium Nitrate - Fuel Oil needs a lot of shock to set it off.

Smokeless powder is supposed to burn according to how much pressure it is under. More pressure the faster it burns. No pressure it burns slowly. I can see if it comes under a pressure spike and is still burning it might really burn fast.

The spikes that popemann recorded happened
after bullet was moving, and slowed down,
then powder speeded back up,and then bullet
speeded up. Pressures of the spikes from
say 70k to 150k, but not astronomical like
a detonation would give, say 3-4-500k or more.
That is why his gun is still together even though it may weaken prematurely.And like you say powder not under pressure burns slower,
we think that popemann's slippery bullets move to easy and to much pressure is lost for a m-sec, thus letting bullet slow, then powder
gets pressure to get it on and you have a pressure spike.And by this time the powder is in turbulance and some may want to go from
conductive to convective, IE the progressive nature that makes a propellant act like a propellant is disturbed..Ed.

.

quote:

There is no propagation of a detonation wave in the combustion medium

ALF, are you saying you do not believe that a supersonic pressure wave is propogated during the decomposition of the gunpowder? You must be using a more restrictive definition of the term that I'm familiar with, but it sounds like you have some experience here.
???

Detonation is generally not that well understood. Probably in some government labs today it probably better understood that 20 years ago.

The shock wave probagates through the explosive and causes the chemical decomposition that is called detonation. Large amounts of heat and gas are liberated. It is my understanding that the heat and gas are liberated after most of the detonation has taken place.

They used to check to see if a detonation had taken place by the use of a "witness plate". A sheet of steel that would have a hole blown in it by the explosive if a detonation took place. That would imply that some kind of explosion like event could take place that would not be a detonation, and it would be hard to tell the difference by just looking.

I think if a detonation took place in a rifle and your fingers were in contact with the barrel you would not have any fingers.

.

I'm surely no expert on this either ALF, but I do think of a rifle barrel as a potential bomb. The explosion inside a bomb is contained until its shell explodes from being unable to hold the internal pressure being developed. The difference in a bomb and a rifle barrel is that the barrel is vented, allowing the projectile and hot gases to escape. Before I shoot, I always make sure there's no obstruction in my barrel.

quote:

Originally posted by McInnis:
I'm surely no expert on this either ALF, but I do think of a rifle barrel as a potential bomb. The explosion inside a bomb is contained until its shell explodes from being unable to hold the internal pressure being developed.The difference in a bomb and a rifle barrel is that the barrel is vented, allowing the projectile and hot gases to escape. Before I shoot, I always make sure there's no obstruction in my barrel.

Another significant difference is that a firearm is charged with a PROPLELLANT rather than a high explosive, the idea being that the projectile will be accelerated out of the bore, rather than blsted out. It is when (IF??) the propellant changes its' behavior from a push to an actual detonation that we are concerned with here. Of course, there are some who say that such occurrences are merely "pressure spikes", and not true detonations such as occur in high explosives.

Have done some research and read where Dupont and the military several years ago expermented with powders and loads in rifles and by going several % points below the 80 % load density level did obtain uncontroled detonation. Where the powder was to be a controled burn all the way out the end of the barrel, the powder exploded all at once causing a huge pressure spike.

quote:

Originally posted by Blob1:
Have done some research and read where Dupont and the military several years ago expermented with powders and loads in rifles and by going several % points below the 80 % load density level did obtain uncontroled detonation. Where the powder was to be a controled burn all the way out the end of the barrel, the powder exploded all at once causing a huge pressure spike.

Note these DOD definitions:

Deflagration: Describes a BURNING of powder or solid grain of 3000-4000 feet/sec. It can be a bullet or rocket motor grain, dynamite, black powder, etc.

Detonation: Describes the high velocity explosion with velocity of 30,000-40,000 feet/sec. It is seen with Class A warhead material or other hgh explosive like Symtex or C-4.

There is another DOD term that was omitted:

DDT - Deflagration to Detonation Transition, used to describe something that used to happen during WWII with aircraft solid-fuel rocket motor elements which were brittle and developed cracks in transit or storage. Sometimes on firing, these rocket motor elements would burn, then detonate. Some have speculated that something similar happens when a reduced charge of slow powder blows up a gun.

Back when I could access DOD research reports there was a report about mixing RDX (C4 Stuff) with propellent for tank ammunition. This mixture actually gave a significant increase in velocity, but they never could get the ammunition to pass their safety tests.

Double base powder does contain nitro-glycerin, and I think this is the suspect in the detonations. However I don't know if gun cotton has some parameters that will cause detonation.