Light powder load + big case= Kaboom?

[RyanM]

I still don't believe that a bullet jammed into the barrel, with a normal charge set off behind it, will actually cause a pressure spike beyond normal chamber pressure, 99% of the time. Especially with handguns, which is the context in which "detonation" is typically raised.

It's basically identical to what would occur if you used a larger volume case (say a .308 Win charge in a .30-06 case, or a 9mm charge in a .357 case), and seated the bullet so that it was jammed tight against the rifling, or with an ultra-tight roll crimp (which will increase pressures due to increased friction, but nothing magical). So that would only be an issue if the powder charge is such that an extra-tight crimp, or seating too long, would increase pressure dangerously; not a safe load to begin with. Isn't some rifle ammunition supposed to be seated so that the bullet is a hair away from engaging the rifling, anyway?

If you've got a bullet acting as a "bore obstruction," and are firing a normal powder charge behind it, there will be absolutely nothing special happening. You just have the equivalent of a larger case, and an extra-tight crimp. That's it.

I'm going to try it out tomorrow, if I have time. TIG welded Glock 23, 180 gr Berry's Preferred Plated hollowpoint, 6.9 grains Power Pistol, CCI small pistol primers, Speer brass. One bullet lodged in the middle, one lodged in the throat, one normal round, and then one with a 10% overcharge. Cases used for lodged bullets will have the powder held in by a cardboard wad. I don't have any fancy pressure testing equipment, so I'll have to go by what the fired case looks like, particularly the primer. Will have to figure out some way of catching the brass.

edit: And now a before pic. O is overload, N is normal charge, X will be bullet in the middle of the barrel, and T will be bullet jammed in the throat.

 

[JackOfAllTradesMasterAtNone]

Hey Blakenzy,

Just go by what's in the published reloading manuals and you'll be safe. Engineers and scientists will always have disagreements.

I'm still trying to determine if anti-lock brakes on my truck are better than non-anti-lock. And if disk brakes are so much better than drum brakes, then why aren't heavy loaded semi trucks using them on all wheels yet?

-Steve

 

[CMcDermott]

Well I can't seem to resist answering JackofAllTrades about disk brakes, so to take this way off topic :

Disc brakes are better than drums because disc brakes function under high heat conditions much better than drum brakes. When the drum of the drum brake heats up, the drum expands and this causes the pressure exerted by the brake shoes against the inside of the drum to be reduced, so the brake doesn't brake as well as it did cold. When the disc of a disc brake heats up and expands, it actually increases the force the pad exerts against the disc so the brake actually brakes better.
Why don't the big 18 wheelers use disc brakes? It may have something to do with the diameter of disc needed - is there a cheap and available material that can take the rotation force of a 24-28" disc without coming apart after it becomes red hot? I think the same cast iron that a drum brake is made of should work, but maybe not. It could be that the manufacturers say that the big trucks have always had drum brakes, and they work (most of the time) and there is no need to try and engineer a air-deactuated (big truck air brakes apply when the air pressure goes down at the brake) disc brake system for the big trucks. Living in Colorado and driving past the runaway truck ramps on the mountain highways and hearing on the news all about what happens when a trucker loses its brakes and control before reaching the next runaway ramp, or is blocked from turning into a runaway ramp by some stupid car driver, provides a constant reminder that the big trucks do need better brakes than the drums that they have now. Some drivers die going off the side of the road in a canyon, some try to ride the truck down on the road; and what happens when a car going 50-60 mph is slammed into from behind by a semi going 70+ usually results in no survivors in the car.

 

[jlh26oo]

liberty

yours was a most interesting post, thanks for sharing your ideas. You are right, we are constantly redefining what we previously thought to be "impossible" (we thought at one time a single "object" could not simultaneiously exist in two different places at once; and less fantastic but even more illustrative of your point- we even believed a 4 minute mile to be "impossible" lol).

The burden of proof is on the person making the claim. I think that's fair.

Not about being fair or not, or who is making what claim first. No absolute proofs of a negative (outside formal systems/languages, ie math, even... nm). However, it takes only one counterexample to prove that it's not impossible (by contradiction). The burden of proof is on those who think the counterexample is possible, fair or not.

 

[RyanM]

Well, the evidence shows that, at least with .40 S&W through a TIG welded Glock, using Power Pistol, and 180 gr Berry's plated hollowpoints, delayed secondary ignition (or something) is a complete non-factor.

It's a lot more obvious in person, but there's definitely a pattern. The overloaded case has the most primer flow into the firing pin hole, followed by the normal case, then the one with the bullet in the throat, then the one with the bullet in the middle has no flow at all.

With light charges of fast burning powders in pistols, I'd say that delayed something is a complete non issue. And also that a blank cartridge, provided that it's loaded with a normal charge weight for the load, not a commercial blank, is a perfectly safe way of unsticking a stuck bullet, from a TIG welded Glock 23 loaded with Berry's etc. and Power Pistol.

If anyone has any ideas for getting the powder to "suspend" in the case, or to otherwise increase available surface area to the priming charge (maybe make a small cone out of rolling paper and put that under the powder, so that the flash hits a cone-shaped area, rather than just the grains directly over the flash hole?), I'm up for testing it next time I go to the range.

 

[Liberty4Ever]

Science is great. I think we have our theories, and that's good, but theories resolve very little. In science, a theory is the first part, followed by designing an experiment to test the theory, doing the test, and analyzing the data. Often, that leads to a new theory, and the process repeats, but each time, we learn something.

I'd love to make a piezo intsrumented barrel and try suspending some medium to small charges of very fine powder of a few different types. There are so many variables it would be impossible to disprove a detonation theory, but it only takes one to prove it can happen.

I'd review the literature to see if I could find the loads (weight and powder type) that are being blamed for a detonation. The chemical and physical formulations are important. Detonation may be impossible in all but one or two types of powder.

I'd probably work up 20-50 rounds of each powder type and charge weight, and devise some way to tap the bottom of the chamber to suspend the powder and then ignite the round, with different timing for each. It'd be difficult to predict when the powder would be at the bottom of the case, when it'd be at the top of the case, and when it would be optimally suspended. Hence the 20-50 rounds for each powder type and weight, and the variable timing before pulling the trigger.

That's a stab at a design of experiment. But even if that's way too much for most range rats, just tapping the bottom of the chamber (with a 2X4?) and pulling the trigger (with a string?) should be a pretty good test with little investment in equipment, assuming it was repeated many times. I'd be tempted to use magnum primers, too, just to stack the deck in favor of a detonation, in case a stronger primer was needed to initiate it.

Stay well clear, because the entire point is to induce a kaboom. It'd be a shame to succeed and die before educating the rest of us.

Similarly, have the video camera going, because you'd have a better chance of convincing many people that you saw Elvis and a little gray space dude riding Nessie that you would convincing people you induced a kaboom with a squib load. Even then, they'll say you just put an overcharge of fast powder in there.

Speaking of science.... Here's a picture from my last range session. I was testing a device I made to reduce felt recoil in my 9mm SUB-2000 pistol carbine. It felt like a lot less recoil on my shoulder, but I wanted objective data instead of a subjective impression. I used a battery powered digital storage oscilloscope to record recoil profiles.


.
.
.

The top trace is the recoil profile (force in the vertical axis and time in the horizontal axis) without the recoil buffer, and the bottom trace shows the recoil profile after adding the recoil buffer. I had the oscilloscope display the amplitude of each and the recoil buffer provides 30% reduction in recoil.

I just loves me some science.

Science and shooting stuff. Does it get any better? It's a whole brain experience. Shooting is entertaining to the primitive brain that likes a little ultraviolence. Science is gratifying to the higher brain functions that desire more rational and intellectual pursuits.

 

[Father Knows Best]

Dude, you are SUCH a geek!

That's cool, though, 'cause so am I. I'd go shooting with you anyday.

 

[Mikee Loxxer]

Libert4ever,

What did you use to generate the voltage for the scope? Some kind of piezo film on the butt with the leads across it's terminals?

 

[Walkalong]

COOl Liberty4ever!

 

[Liberty4Ever]

What did you use to generate the voltage for the scope?

I used a .75" square force sensitive resistor (FSR), in a voltage divider. I actually haven't calibrated it yet, but the force-resistance curve is reasonably linear except near the extremes (no force and overload force). The bottom of the butt plate was the part that seemed to be causing most of the recoil impact, so that's where I measured the force.



I plan on recreating the test with more rigorous science and calibrated instrumentation, but this was a good first test to verify that my optimism about the recoil reduction wasn't shading my subjective assessment too much. The super-resilient elastomer buffer cylinder does make a big difference in the recoil.

You wouldn't think a little 9mm carbine would kick much. It's no 12 gauge or anything, but it's so fun to shoot I can put 400 rounds through it before I know what happened, and the next day the shoulder can be a bit tender. Not any more. I'm planning to get a 40 S&W version too, and it kicks quite a bit more. I also made a recoil reducing butt pad. Add that to the buffer cylinder and it's a real pussycat.

The little Kel-Tec SUB-2000 is surprisingly fun to shoot.

I was a bit surprised when I compared the recoil profiles. I expected the buffer cylinder to store a bit of energy to reduce the peak recoil spike and then release the energy, so the recoil energy is distributed over time as more of a gentle push than a sharp slap. I expected the area under the curve to be about the same, corresponding to the same recoil energy, only redistributed for less of a peak force. But the timing looks almost identical with the magnitude lower. Apparently, the super resilient buffer material provides a fairly inelastic collision when the heavy bolt flies back and hits it, and a lot of the recoil energy is absorbed and converted into heat. I need to do some calculations, but the buffer cylinder doesn't get very warm, and it hasn't shown any signs of breaking down in over 1000 rounds.

These recoil curves look different than I expected. I had seen recoil curves from bolt action rifles, probably measured with a piezo sensor or maybe an accelerometer. They were smoother and were more of a rapid spike with an exponential decay. The recoil curves I measured were essentially square pulses with negative spikes at the transition points before and after. The squared off tops seem odd, and I'd suspect that the sensor maxed out and clipped the data, except for the fact that the recoil buffer disk version had the same shape and the flat portion is almost two volts lower, so it doesn't seem to be clipping.

This is preliminary data, and I started not to even upload it, fearing it'd generate embarassing questions and I wouldn't have the answers. It was almost dark after a long range day when I finally collected the data. I'd have liked another hour to collect a lot more data and get a better feel for the instrumentation and the data. Next time, fer sure!

Science is fun!

Shooting stuff is fun!

The other big news of the day was the special 9mmSUB loads I created. My goal was the fastest bullet I could get out of the little SUB-2000 without exceeding a +P load. I used a light 90 gr Hornady JHP XTP (intended for the .380) and I loaded a lot of slower Longshot powder behind it in some +P brass. I gradually worked up to the load, to make sure I had no overpressure signs. From the recoil, I'd guess these were +P loads. 1932 FPS. Yeow! That's 746 ft lbs of kinetic energy, the same as I get shooting the very hot Double Tap 165 grain defensive loads in my 10mm Glock, and about the same as the .223 loads I shoot in the PLR-16 pistol.



I already did some crowing about this in the reloading section of THR, under the tread about 9mm Rifle Loads a few days ago.

http://thehighroad.org/showthread.php?t=242909

No practical use I can imagine. The light hollow point would probably fragment like crazy at that speed. Maybe a long range SUB-2000 round, where the accuracy of the carbine could be utilized, and enough velocity would remain for the hollow point to expand, but I think the 115 gr SUB-2000 load at 1652 fps would probably be better for longer distance. Actually, based on recoil, that might have been a bit more than a +P load, although still no signs of overpressure.

 

[.38 Special]

Vern Humphrey

Thank you for finding that article again. Good stuff. I suppose we have a bit of a semantics issue -- not to mention my guilt at not reading your orginal post as thoroughly as I ought to have -- in that I do not consider "squib load detonation" to be the same phenomenon as "secondary explosion effect". I believe you noted something along those lines and I was too busy leaping to my keyboard to catch it.

 

[Alpacca 45]

Here's a Newby jumping into a contoversy:

Go to the gun's cooled, lubricated, and more frequent firing brother the car and truck engine.

The loads are much smaller, a typical firing of a 1 litre capacity cylinder is going to burn say 1/4 of a drip of the fuel you'd get by dripping it out of an eye dropper, it's not exact, but it is that sort of order.

Petrol engine designers go to great lengths to avoid detonation (knocking / pinking) with squish zones in the combustion chamber, sodium filled valve stems and correct "heat" spark plugs and aluminium pistons to avoid hot spots, and compression limited to allow running on the available octane fuels. Why? because detonation will hammer the engine to death.

Disiesel engines, or at least the ones up to now have had to be built much heavier to withstand detonation. detonation of the full charge of injected diseisel sometime after the injection finished is what made some disiesel car engines (VW were attrocious for this) so rattly when they were cold.

Detonation is the progression of a reaction front at the speed of sound in that material. It can't go faster than the speed of sound in that material, but the speed of sound can be made to be faster...

The "power" of an explosive is really down to how fast you can get it to release its energy, obviously some explosives will have more energy to release for a given weight being detonated, but assuming a given calorific value, then the power depends on velocity of detonation.

I haven't got my text books with me, so there are no nice formulae or learned quotes to give, I'll try to do it with examples instead.

ok: velocety of detonation is equal to speed of sound in that material, what makes the speed of sound change?

Speed of sound is proportional to density, increase density and the speed of sound increases too (example, speed of sound in air decreases with increasing altitude. Speed of sound at sea level is around 1100 feet / second, go into the sea ( density increases again) and the speed of sound is closer to 3 times that in the air above)

In solids, speed of sound is also increased by having a continuous solid, velocety of sound in sandy soil is barely 3,300 feet per second, in really stiff boulder clay it is more like 10,000 feet per second.

It also increases with rigidity / stiffness, think of how a hardened steel plate rings when it is hammered compared to a softer plate?

OK, putting this in terms of explosives:
old prilled ammonium nitrate with fuel oil absorbed in it has a lower velocety of detonation than an ammonium nitrate / fuel oil emulsion, primarily because the emulsion is denser and continuous and so has a higher sonic velocety.

This can actually go too far with ammonium nitrate emulsions and most other explosives, if the speed of sound gets faster than the rate of reaction, then the energy runs away ahead of the reaction and the detonation dies out, this is called "dead pressing". in commercial ammonium nitrate emulsions this is cured by mixing in polystyrene foam granules to reduce the density (hence the speed of sound) they also have an additional effect that as the granules are compressed, the gas they contain flashes to white heat and gives additional points of ignition.

Next time you read a description of nitroglycerine as a dense liquid which has a high velocety of detonation (as though the two were completely unrelated) you'll be thinking "well duhhh, if it wasn't dense it wouldn't have a high velocety of detonation or be a powerful explosive..."

Back to guns going Kaboom

I don't know whether this works in practice, but here's how it might in theory:
None magnum primer in big case with severe underload of ball powder fails to get it burning properly, but it does start the stuff decomposing to a mixture of red nitric oxide fumes, sooty carbon monoxide and hydrogen.

These are corked in behind a bullet, and you have say 20 0r thirty grains in a magnum rifle case, this is a far, far greater amount of energy than in the 1 litre capacity automobile engine cylinder.

at some point, pressure in the gas (PV=nrT) results in the temperature rising high enough for dieseling to begin. because you now have 20 or thirty grains of gas in a small case ( high pressure and density) the detonation front travels very fast, energy is released faster than the bullet can get out of the way to relieve it and the shock wave reflecting from the free outer surface of the barrel sets up tensile stresses sufficient to split the steel of the chamber from the outside and propagating inwards.

A while back, varmint al had some links to some guys making stress guage chamber pressure monitors. some of their pressure recordings were showing two pressure peaks with big pressure spikes coming after what should have been the max pressure.

As I say, I don't know whether it happens in practice, but that is how I would see the mechanism working.

Remember that with each cylinder of an auto engine firing 400 times a minute at idle and say 3000 times a minute flat out, you still don't get many knocks a minute when detonation starts, so with the marginal conditions for it happening in guns, perhaps we are not firing enough dodgy loads to repeat it reliably in the lab.

 

[Vern Humphrey]

The only instance I know of "detonation" in a firearm being observed in a laboratory setting was a 6.5X55 Swedish Mauser. It showed exactly that two peak pattern. The conclusion is the primer flashed over the powder, which ignited a fraction of a second later. In the meantime, the primer alone had been enough to drive the bullet into the lede, where it stuck, forming a bore obstruction. The result, of course, was not a "detonation" but a pressure event.

All these "detonations" show the same signature -- the streteched and deformed metal of a pressure event, not the shattered fragments of a detonation.

 

[LightningMan]

JimWatson Quote;
There was one on the SASS Wire a while back about the light load that just MUST have detonated to wreck a gun, the Perfect Reloader would not have made a stupid mistake like a double charge. But they kept investigating, kept running his setup, and found that sure enough, he had not double charged the POWDER, but had likely loaded two bullets over one charge. A bullet had stuck in the seating die, glued by bullet lube, and he had set another and rammed both down in the next cartridge

I have been a witness to a single action detonation, and it was a very strange phonomenon, as it only sounded strange, not louder just different. Don't know the story behind that one, but I personally have had the above situation happen. I caught it before anything happened, and also a friend of mine had it happen to him, which the only thing that saved his Colt SAA is that 44-40 round would not chamber. He took that round apart and found 2 bullets in the case! So if your reloading on a progressive and find spilled powder & a empty case in you tray, you most likely have a loaded round with 2 bullets in it! BE CAREFUL! LM.

 

[Ky Larry]

Read the book, understand the book, obey the book, be careful, triple check your powder level in each case, pay attention and you will not have a problem. Knock on wood, I've been reloading since 1974 and haven't had a Kaboom yet.

 

[Slamfire]

Oldie but goodie.

Powders don't burn linearly like matches. Powders also produce pressure waves, which could get out of phase and cause problems.

There is a long section in P.O. Ackeley's book on problems with reduced loads in rifle cases. The powders used were reduced charges of slow burning powders.

Rifle cases have a lot more volume than pistol cases. But still I believe if you want to shoot ultra low velocity loads in pistols, you are better served by powders like Trail Boss. Which is very bulky and fills the case.

Even though I do believe that most blowups are due to poor process control on the part of the reloader, strange things happen.

 

[Archie]

I Have Before Me a Book...

Firearms Pressure Factors, by Lloyd E. Brownell, Ph.D., and several assistants. Published by Wolfe Press in 1990 (ISBN 0-935632-85-9).

Dr. Brownell seems to believe there is a phenomenon regarding small charges of relatively slow burning powder in large cases that causes firearms - primarily rifles - to blow up. Conventional handgun rounds do not seem to be subject to this event.

The event seems to be restricted to rifles, specifically rifles with larger cases (not much in .32 WCF or .35 Remington). There are several theories, but none that will reliably blow up a gun on command; so the event isn't completely understood. Having said that, there are instances of rifles coming apart seemingly as the result of a smaller than normal charge of slow burning powder. Dr. Brownell's reseach - with pressure systems and oscilliscopes - did in fact show up some curious and unexplained pressure 'excursions' where spikes of pressure occurred during the testing.

On a similar subject, the late Julian S. Hatcher did some testing on the effects of powder position in a case. Again, with rifles only - the .30-06 military round, I believe - identically loaded rounds with powder charges that did not fill the case where chronographed with the rifle held level and shaken to distribute the powder through the case, and then with the rifle held muzzle up prior to firing and carefully brought to level. In all instances, the rounds with the powder near the primer gave greater velocity. Without question the position of powder in the case has an effect on the pressure curve.

On top of whatever else is known or suspected, slow pistol powders like 2400 or H110 simply don't give very good results when loaded 'lightly'. So, one should stick to fast powders for light loads and ensure no double charges. If one desires to experiment, do so with safety precautions in place and try to video tape the experiment, so the rest can see what happened if one is not available to comment.

 

[Vern Humphrey]

If one desires to experiment, do so with safety precautions in place and try to video tape the experiment, so the survivors can see what happened if one is not available to comment.

Fixed it for you.

 

[Conservadude]

The post about why not to use light loads H110 or W296 needs a tune ...the reason for not loading those two powders into a light load is because they (they are the same) require higher pressures in order to burn completely. Light loads will result in possible squibs, leaving a bunch of yellowish little granules of powder all over your gun, etcetera ...but not a secondary detonation. The only powder the I have heard of that might produce a bigger bang than expected is Trail Boss, and I checked into it with the manufacturer. They said that you want to avoid crushing the powder, but otherwise use whatever amount you want and that the max load is a full case, period. That was for my 500 S&W, BTW. The reason for not crushing it is because it's made of delicate little Cheerios or donuts and crushing a bunch of them may result in a faster burn rather than the controlled burn it was designed to produce ...and that's still not a detonation. And you'd really have to TRY HARD to damage the powder enough to cause an issue. I think that light loads risk double loads not spotted by the reloader and that's where the trouble and rumors have come from. Your reloading procedure should be designed to prevent double loads, e.g. examine 50 open (charged) cartridges at once using a bright overhead halogen light ...any that are low or high stand out immediately. When in doubt about a powder or worried about internet rumors, call the manufacturer and ask. If you're still scared, use a powder that is advertised to produce position-independent ignition, something like TiteGroup for example.

Brian

 

[Samgotit]

edited

 

[alsaqr]

In the not so distant past field artillery guns were destroyed when shooting small charges of slow burning powder. This phenomenon is well understood by those who develop field artillery propelling charges. In the case of field artillery this has been replicated.

The older propelling charge for the 105mm howitzer contains seven increments. Each increment is contained in a cloth bag. Increment 1, the base charge, is attached to the primer and cannot be easily removed. Unless the gun is to be fired at near maximum range some of the increments will be discarded.

The lower charges consist of small grain, fast burning propellant. The higher charges contain larger grain, slower burning propellant.

 

[Double Naught Spy]

In the not so distant past field artillery guns were destroyed when shooting small charges of slow burning powder. This phenomenon is well understood by those who develop field artillery propelling charges. In the case of field artillery this has been replicated.

Citation?

 

[alsaqr]

Citation?

My conversation with Dr. Gerald Bull in 1988.

 

[Double Naught Spy]

In other words, nothing that can be referenced. Got it.