During a discussion on the thread about a KBoom to an AR, the possible causes were discussed and ammo was the most popular choice. However, not everyone agreed to how the ammo could be the culprit. One notion was a lightly loaded cartridge could cause over pressure enough to cause the KBoom. I had heard something along this line a few years back and decided to check it out. This is the result of a little research/web search for some validated info on how an underloaded cartridge could cause a such as the AR to disassemble itself in a spectacular fashion.
Okay Stinky Pete, here is the research I promised you. I did most of the leg work but the last link is really long so you all will have to go there and read it. I included the web address with each reference I found.
Another good guideline for a starting load density is 85% with an appropriate powder. And never build any reduced loads with slow burning powder. The best loads are with powders that nearly fill the case. (LD= PC/WV.) LD = loading density, PC= Powder charge in grains, WV= Water volume behind the bullet in grains
M. D. Smith did an excellent experiment using light loads and repositioning the powder in the case to demonstrate the effect of uneven burns and pressure waves on exterior ballistics. In short, powder positioned by the primer produced consistent velocities while powder positioned by the bullet produced very erratic velocities. These results are consistent with current Interior Ballistics thought.
The interior of a cartridge in combustion is not an ideal gas at rest. There is a flame front, pressure waves, and two densities of content present (air and powder/air). As you know, sound waves propagate through different densities at different speeds. It is a complex environment to model, and no single physical rule is sufficient.
Generally speaking, an air gap in a cartridge causes the flame front to extend quickly over the exposed surface of the propellant. Because of gravity, this air gap (and flame front) tends to be along the top of the powder, because the powder has settled along the bottom.
Some powders work well in this situation, like a little Bullseye in a big .45 Colt case. It has lots of room to expand and quickly reaches peak pressure and complete combustion, resulting in an economical and efficient load. Bullseye is a double-base powder with lots of energy content and little or no retardant. It needs little more than a spark to ignite it.
Slow single-base powders or heavily retarded double base ball powders need pressure, not just ignition heat, to burn well. They generally burn well in a full case with no air space (other than inter-powder space). In cold conditions, with weak primers, and/or low pressures (light loads) it is quite possible to get a "bad burn" (large percentage of propellant never ignites.) This manifests itself in erratic velocities, hangfires and so-called "bloopers".
Occasional detonations of light loads of slow powders was well debated in the 50's and 60's and is now an accepted fact of interior ballistics. They are easier to understand given the facts above, and the fact that most energetic materials have two burn rates, a deflagration rate and a detonation rate. Propellants are distinguished from explosives (by the knowledgeable, anyway) as energetic material being consumed at its deflagration rate. Explosives are self-consuming at their detonation rate.
Most energetic materials can be consumed at either rate, given certain circumstances. Dynamite lit with a match will produce a blazing bonfire, but no explosion. Expose it to the concussion of a blasting cap and it will detonate. Light it with a match in an small, unvented closed chamber (called a "bomb") and it will transition from deflagration to detonation once the pressures get high enough (assuming it is not already completely consumed.)
Detonations of small charges of slow powder work the same way. They deflagrate (relatively) slowly. Often pressure waves move the powder around and pack it against the base of the bullet. Single base extruded grains often break and are crushed by the slowly rising pressure. Now propellant is burning front-to-back, where it was burning top-to-bottom and/or back-to-front.
Pressure waves then bounce back and forth along the case, sometimes meeting each other in opposing directions and producing peak pressures nearly twice the expected, given the volume of gas. This impact or concussion sometimes pushes the burn rate of the propellant into its detonation rate.
Modern reloading manuals warn against reducing loads of W296 and H110 in magnum pistol, and H4350/IRM4350 and slower in magnum rifle, for this reason.
The .308 and .30'06 are relatively immune to this phenomenon for two reasons. One, the exposed surface of the base of the bullet is fairly large compared to the case volume. Given the same crimp and debulleting force required, debulleting occurs sooner than in a .308" than a .277" because at "X" PSI there is more square inches (or fractions thereof) of bullet base for the gas to push against. Debulleting considerably moderates unfavorable pressure wave situations by increasing chamber volume (lowering pressure, giving pressure waves longer travel, etc). Chamber volume increases quicker in a .308" bore than a .277" bore for each unit of bullet travel because of the four-fold increase in bore volume for each corresponding increase in bore radius.
The second reason is proximity. The cases are small enough that either primer spark, or the primary flame front will reach all the powder relatively soon in the sequence of ignition. When a significant amount of powder packs-up in the front of the case, unignited, the chances of detonation greatly increase.
Understanding all this aids the reloader in choosing the proper burn rate for each cartridge and load, though some experimentation is always worthwhile
Hope this answers some questions.
Yes, yes I'm familiar with this work. 1) In my world, 2400 is a SLOW burning powder! 2) The effect can not be reproduced. WHY NOT? I believe in science. Science says if you do everything EXACTLY the same each time, chemicals react the same way. Now, perhaps there is some detail, but we know about powder position. 3) After a kaboom, the powder is destroyed. To claim that too little powder did this, without reproducable verification of the claim, is the same as claiming normal cartridges just Kaboom sometimes, without reproducable verification. I believe in CAUSALITY- things blow up for a reason, not a superstition. 4) Direct experiment and personal experience. I have loaded plenty of superlight loads, and here I am. NO KABOOMS. Another fella on this board did the same thing. No kaboom. I will grant you that you get crappy results using slow powders, and I do agree that there is significant risk that I may be wrong- so I use very fast powders and cast lead bullets for light loads. 5) Contradiction of expert opinions- the Cast Bullet Association now recommends AGAINST using dacron filler! Dacron filler is no longer recommended because.... I have no idea. I still use it it tried and true loads. I think they want you to use cornmeal filler or nothing at all now. And butter is better for you than margarine... for now! 6) My limited understanding of science tells me that gunpowder is completely turned to gas, and very quickly. We get a certain amount of energy per chemical bond, no exceptions. If I have 1/4 the powder, I get 1/4 the energy. NO EXCEPTIONS. In detonation, the pressure peak rises very fast, and ends very fast. The total energy is the same as for a light load, and to move metal, we need to do work. Perhaps there can be subtle high velocity effects on metals... but they should be reproducable! 7) Occam's Razor - a principal in Logic that says if you have two reasons for something that have equal evidence, and one is simple and the other is very complex, then the simple one wins. Example; 1) The cartridge was underloaded, and it was freakytime, so it blew up. 2) The bullet was loosly seated, and when it was chambered, the bullet had been pushed back so the COL was something like 1.9 inches, which caused an overpressure situation. I'm not advocating case 2. It could be anything, since we are just jawing at the fencepost here. I know for a fact that if I seat a bullet improperly on a healthy load, it WILL overpressure EVERY TIME. OK, OK.. WHY DO I GIVE A CRAP? Well, I like this place. I like all you guys. Who else is interested in this stuff? But haven't you guys got a little skepticism about gun experts yet? - Experts said 5.56 would not work as a combat round. That it could not compete at distances over 300 yards. That you could not shoot anything over 70 grain bullets. -Experts said that .45 Long Colt brass was too weak to contain the pressure of a .44 magnum- that the brass would fail, and everyone would weep bitter tears. I think Jack O'Conner may have started the fable, or maybe even Saint Elmer Keith. Well, me and a lot of other guys load .45 Colt brass with Casull loads, and shoot them in Casull guns, because there is no problem doing so whatsoever. I load my Ruger .45 Long Colt to pressures that are almost tripple the maximum published loads for .45 Long Colt. Know what? There is no problem. Know why? Because some real smart Cowboys looked at how much steel was in the Ruger, and looked at the steel in the .44 magnum and did the math. Literally. Then they got out sandbags and string, and started loading up. Hmmm. Then they sent guns to White labs, and had them find the load that caused failure. It's only just now becoming accepted that Rugers and T/C's can easily handle loads that would blow a new Colt in to a wreck of twisted metal. Yup, the Ruger weighs a LOT more than a Colt. Most people will still tell me I'm going to die if I shoot 20 grains of H110 with a 255 grain bullet out of a .45 Colt, even a Ruger. Hasn't happened yet, to a large crew of sixgun hunters. Finally, Hodgdon really warns upsidedown and backwards about H110 and Lil' Gun pistol powders. DON'T REDUCE LESS THAN 5%!!! OK, did you guys know that the internal capacity of a .45 Long Colt and a .454 Casull are exactly the same? It's true. Exact same internal diameter, same internal length. The Casull brass is a tad longer, but the COL is the same--- the extra brass is just used for extra crimp. The maximum load for a 300 grain bullet for .454 Casull is like 31 grains. The maximum load for a .45 Colt(ruger) is like 21 grains. Reduce it 5%, so 20 grains should be fine. Wait a second! Can the powder read the headstamp? Same bullet (identical), same internal volume (same diameter and length), and yet 20 grains is PUBLISHED to be SAFE!!! 20 grains is 64% of 31. Yep. Oh, they don't publish the same bullet weights anymore all in one place, but I have a lot of old reloading manuals. So, color me skeptical. Detonation doesn't make sense to me. I would like to see it for myself- under controlled situation. I would also never load light with a slow rifle powder. It's not worth the risk because I can be wrong- I'm often wrong- but also because there are much better performing powders for light loads. Anyway, I hope somebody enjoys this long ramble. And that's it for me. My parts arrived, and I'm done going stir-crazy Pete
>Experts said that .45 Long Colt brass was too >weak to contain the pressure of a .44 magnum- >that the brass would fail, and everyone would >weep bitter tears. I think Jack O'Conner may >have started the fable, or maybe even Saint >Elmer Keith. I suspect that in the days of Elmer Keith and Jack O'Connor, there were a lot of balloon-head cases floating around. Those are considered unsafe for modern high-pressure loads. My understanding is that exceeding maximum pressure causes permanent damage to the metal; I would worry more about the gun becoming too weakened to fire normal loads than I would a sudden catastrophic failure. jafager
You prove my point, exactly. 1-Perhaps these guys were thinking baloon head brass- except they never mentioned it. ANY baloon head brass is unsafe with modern smokeless powder. 2- Finally, so many people are doing it and so much data has been acquired, most powder mfgs. now list separate loads for Ruger and T/C .45 Colt that WILL blow a traditional (but new and good shape) Colt to bits. I agree that full power loads will reduce the life of my Ruger .45 colt revolver... reduce it to the exact same gun chambered in .44 Magnum that shoots full power loads! HAH! It'll outlast me, and anyone old enough to read this. [url]http://www.hodgdon.com/data/pistol/45coltlil.php[/url] 3- As for using .45 Colt brass in Casull, Paco Kelly has been doing it since the first .454 Casulls came out, and brass was not available. It worked, and he just kept using it. He gets just as many reloads with .45 Colt brass as with Casull brass- both loaded to Casull maximum loads. We are talking about many years and many thousands of rounds. Here's en exerpt from a Paco Kelly artical called .45Colt/.454 Casull: "...I purchased 100 brand new 45 Colt cases..(Freedom Arms doesn’t recommend you use 45 Colt cases for 454 loads) I loaded them 14 times each...with NEI’s 290 grain Keith bullet over 30 grains of 2400....I have no idea what the pressure is or was but the velocity was near 1700 fps from a 4 and 3/4 inch barreled handgun...I lost one case...I crushed it in the reloading press...so much for those that say 45 Colt brass is weak. All of those guns shot with accuracy I had never seen in handguns before, especially with such heavy loads. Holt and I got so used to the superb accuracy that when one gun kept stringing it’s groups just 1 and 3/4ths of an inch..we sent it back with the targets...Dick Casull himself took the gun off the line as SUBSTANDARD in accuracy. The gun I purchased (with a then a bank loan of $620) put five rounds into ½ inch groups..the other twelve guns were all close in accuracy..Holt’s gun shot easily into 3/4ths inch groups....these were open sighted guns at 25 yards... Holt did all the testing with the scoped guns he would have to tell you about those. But I didn’t stop there...in ten years plus, not quite 11 yrs, I put over 70,000 rounds thru my gun. 95% were cast loads...I have had the throat insert in the barrel, replaced twice. And the ejector rod kept coming off after all those rounds...so two years ago Bob Baker, Freedom’s President, and a handgun hunter in his own right, took my gun back to the factory with him from the gathering of the Shootists. When I got it back several days (not weeks) later I tried to shoot the rod off again...with 340 grain SSK bullets at over 1600 fps...after two hundred rounds in two days and no problems...I figured they got it right. Now you tell me in all honesty what handgun in America today will take 6 to 7 thousand rounds of heavy loads a year...and have only the ejector rod come off after ten years?!. Sure barrels will wear out...but the special insert that Freedom puts in their Primer Grade guns is changeable...And 95% of the loads were cast bullets, with non-ball powder. By the way that’s over 3000 lbs of lead and 290 lbs of powder over a ten plus year period....that’s about five hundred plus rounds a month for near 11 years. Some years more...some years less..Today I fire about 2500 rounds of handgun ammo a year, in all kinds of calibers....the hands and the eyes are getting old...." Note: Paco knows what the pressure of his load is- it is a HEAVY casull load! So... what do you chose to believe, and why? Next, tell me about how my muzzleloader will blow up because I use smokeless powder. YOUR muzzleloader WILL blow up if YOU use smokeless powder! I gaurauntee! Mine is the Savage, designed and built for smokeless, and pressure tested to over 170,000 PSI. Yet people tell me all the time I'm going to blow up and weep bitter tears from my dead eyes. Yet here I am. I still say "Safety FIRST, SECOND and THIRD"- but to me that means knowing what I'm doing, and taking responsibility for it. Not blindly following so-called experts. Pete
Wow, SP, you sure did let go with a fusillade of words. And I agree with you on most points. I merely wanted to point out that there were plenty of experts out there saying that light loads can and will cause KB's. In the case we were discussing, my opinion is that the ammo WAS lightly loaded, so that the powder charge was below the primer hole. One magnum primer and and all of the exposed powder is burning at once. This is what caused the over pressure condition and KB. My opinion is based upon fact and observable phenomena. First of all, modern smokeless powder has a varying burning rate that is controlled by the pressure exerted on it. Example, pour a charge of powder out on the ground and ignite it. It burns for a brief but measurable time usually in seconds. Put the same charge in a cartridge and ignite it and the burn rate increases significantly, and is measured in milliseconds or faster. Secondly, the powder charge in a normally loaded cartridge burns linearly from primer end to muzzle end. I base this on observing unburnt powder being ejected out the barrel with the bullet in the firing of heavy powder loads. When the powder is below the flash hole, the entire surface area of the powder is ignited. Since this surface area of burning powder can be significantly larger than that of the normal cartridge diameter, the peak pressure is reached must faster. Normally, the peak pressure is controlled by the increase in burning chamber volume caused by the bullet going down the barrel. This is one of the considerations that is taken into account when developing loading data for any cartridge. If the pressure increases at a much faster rate and the bullet movement cannot regulate it, then a dangerous peak pressure condition could exist. This is what I believe happened in the case in point. The pressure caused the case to rupture and the escaping gasses damaged to rifle as seen. I believe my opinion will satisfy your quest for causality, by pointing out the observable and measurable factors it is based upon. Verification can be done through testing, but I do not have a pressure test fixture with which the tests could be performed. And I'll surely not use one of my black rifles to prove this point. So, in the interim, I will just make sure that all of my ammo is loaded properly and comes from a reputable and trustworthy source.
Knowing nothing, I have heard two possible explainations for this phenomenon that seems reasonable. The high pressures of the powder being ignited abnormally (eg. all at once), or a squib load with insufficiant energy to propel the bullit out of the barrel. If un-noticed, the shooter shoots again with the prior bullit still lodged in the barrel and.... Well, sounds good anyway.