Undercharge blows up a Model 64 -- need explanation

[Rafter-S]

Gentlemen,

My gunsmith pal had a Model 64 S&W revolver in his shop today that had the cylinder peeled back like a banana, and the top strap humped up. I asked how much was the overcharge. His reply was it was an UNDERCHARGE of powder, with a short, light weight bullet not being set back in the case far enough.

I have heard about this over the years but never actually seen a gun it happened to until today.

Speer Reloading Manual Number Nine says it's a "phenomenon," or at least it was 35 years ago when that manual was published. Has there been any scientific explanation since? Does anyone have a link to a formal study where it is explained what takes place to do this?

Thanks in advance,
Rafter-S

 

[Big Cholla]

The small amount of powder does not have sufficient mass to cause the burning rate curve to take the 'normal' amount of time to max pressure. The burning rate curve instead is greatly accelerated to max pressure in far less time than normal for that cartridge design. The result is that the bullet does not have enough time prior to max pressure being reached to get moving down the barrel relieving pressure as it moves. Ideally the bullet should be nearing the end of the muzzle at max pressure. Instead the bullet becomes a 'plug' with no movement in time to relieve the developing pressure. In effect a miniature explosion occurs instantly within the cartridge with a resulting overpressure to the cylinder walls. Certain powders are more likely for light loads to detonate than others. ........... Big Cholla

 

[Alk8944]

It would be interesting to know what powder was being used.

This has been happening for the past 45 years or so, usually with relatively slow ball type propellants. The usual suspects over the years have been 630, 630P, 296, H-110. There is enough anecdotal evidence that both Winchester and Hodgdon (296/H-110, same powder) have finally published advice to only load these at the recommended maximum charges or not reduce more them 3% by weight. They are recommended for magnum cartridges (.357/.41/.44 etc) which have a SAAMI MAP of ca. 36,000 PSI. Reducing these by 3% would still produce pressures in the ca. 33,500 PSI range. They are not, therefore, suitable for .38 Special or other cartridges having SAAMI MAP specifications less than the above 33,500 PSI or close.

This has been duplicated in the laboratory, but infrequently. It is extremely hard to reproduce in a controlled environment and for quite a few years the manufacturers vehemently denied that it was happening, or could. There have been several terms invented to describe this, among which are Secondary Explosion Effect, Pressure Excursion Effect, Detonation, etc. I have not yet seen an adequate explanation, just several theories, none of which has satisfactorily explained the situation.

 

[nuubee]

Hi,
This is my first post here (just joined recently). I'm not sure that I understand it on a very technical level, and I'm sure that most of you are far more knowledgeable than I, but this is what I seem to recall reading a long time ago. A smaller amount of powder in the case leaves more space, and exposes more surface area of the gunpowder. That means that the flame coming through the flash-hole is able to ignite more of the surface of the gunpowder all at once than it normally would, which can create a pressure spike from the expanding gasses, instead of a fuller load causing less powder being ignited at the same time, and then combusting in a more controlled manner.
I haven't done much shooting lately, and I haven't done any reloading in years, but the first time I read that, I was loading small charges of Bullseye powder in .357 cases, and after that I started putting in very small tufts from cotton balls, to force the powder charge back against the primer, even when the case was horizontal in a gun. I have heard of other people filling up their cases with flour, on top of very small powder charges, although it does seem like that could affect internal pressure also.

 

[TAROMAN]

Or using Trail Boss, which fills up most of the case.

 

[BUFF]

Decades ago, the NRA hired H.P. White Labs to investigate "detonation," as the catastrophic explosion of small charges of fast powders was termed.

H.P. White said that the typical suspect, 2.7 grains of Bullseye, usually under a 148 grain bullet in a .38 Special case, didn't posess the chemical energy to destroy a revolver, no matter how fast it ignited. They speculated that the destruction is probably usually caused by unintentional double or triple charges of powder or by two bullets seated into the same case or by two bullets over a double charge, probably from inattention or mistakes made on a progressive press.

It took 2 bullets and a double charge for them to reproduce what they had been shown by end-users.

This did not include incidents of folks using very light charges of slow speed rifle powders, just quick pistol powders.

 

[Skip Sackett]

Decades ago, the NRA hired H.P. White Labs to investigate "detonation," as the catastrophic explosion of small charges of fast powders was termed.

It took 2 bullets and a double charge for them to reproduce what they had been shown by end-users.

This did not include incidents of folks using very light charges of slow speed rifle powders, just quick pistol powders.

I can tell you this, I spoke to Hodgdon and they don't believe in "detonation".

I asked specifically about it the last time I had a question about powders. I spoke to them about H110/W296 and light charges and what was the problem with doing so. They assured me that "detonation" was an urban legend as far as they were concerned that sticking a bullet in the barrel and chasing it with a full power load was much more likely and dangerous.

FWIW

 

[n4zov]

I don't have a clue about what happened in this particular case, but I would bet on a double-charge rather than "detonation," a cosmic alignment of the planets, or any other unproven theory. Unless somebody has laboratory repeatable proof that something unusual happens with small charges of fast burning powders, I'll stick with the most obvious and likely answer - a double charge.

 

[TSQUARED]

I have read about the detonation of light charges of very slow burning powders but personally I would bet that the gun was blown up by a double charge or an obstruction or a combination of both.

 

[MMA10mm]

Decades ago, the NRA hired H.P. White Labs to investigate "detonation," as the catastrophic explosion of small charges of fast powders was termed.

H.P. White said that the typical suspect, 2.7 grains of Bullseye, usually under a 148 grain bullet in a .38 Special case, didn't posess the chemical energy to destroy a revolver, no matter how fast it ignited. They speculated that the destruction is probably usually caused by unintentional double or triple charges of powder or by two bullets seated into the same case or by two bullets over a double charge, probably from inattention or mistakes made on a progressive press.

It took 2 bullets and a double charge for them to reproduce what they had been shown by end-users.

This did not include incidents of folks using very light charges of slow speed rifle powders, just quick pistol powders.

As relates to HANDGUNS which typically have very low expansion ratios (big bore diameters with cases of approximately the same size so there is no shoulder on the case), everything I have read and studied, including those HP White tests, indicates that there is no "detonation" or "Secondary Explosive Effect" possible. Blown up handguns are always the result of multiple powder charges or stuck bullets in the bore.

In rifles, the question of detonation (or S.E.E., whichever you prefer) is still a very real possibility. In those circumstances there is always a LOT more powder being burned, it is slower-burning-rate powder, there is a very high expansion ratio (small bores with huge powder supplies behind it - at least when compared to a handgun cartridge), and there's usually no way to get a double or triple charge in the case. Western Powders highly recommends against reduced loads with their rifle powders, and they have a cut-off of 78% load density. (In other words, if a particular load with a particular ball powder of theirs ends up being below 78% for the starting charge, they won't publish nor recommend that load...) They cite "poor ignition characteristics" for their reasoning. I think it's because of S.E.E.

There has been a lot of articles in Handloader Magazine about this circumstance over the years, and it's never really been 100% pinned down as to cause.

 

[Dennis The B]

Some time ago, I read that one of the reasons for pressure spikes, especially in small amounts of high-speed powders, was that the primer ignition caused a flash-over. That is, the powder laid flat in the case, and the front of the charge ignited, starting the bullet through the forcing cone, and down the barrel. Later (milliseconds), the balance of the charge ignited, and the bullet in the barrel failed to move any further forward. The balance of the ignited charge was enough to bulge the barrel, and perhaps damage the cylinder.

This phenomenum also happens in light black powder charges. That's why people have used fillers in black powder casings. When I was shooting black powder cartridge, I used corn meal as a filler, beneath the wad, so I could have enough volume to completely fill the case. In my case, I was using some 405gr bullets in a .45-120 Sharps, and using 70-80gr of FFFg powder.

 

[Last of the Mohicans]

Hi,
This is my first post here (just joined recently). I'm not sure that I understand it on a very technical level, and I'm sure that most of you are far more knowledgeable than I, but this is what I seem to recall reading a long time ago. A smaller amount of powder in the case leaves more space, and exposes more surface area of the gunpowder. That means that the flame coming through the flash-hole is able to ignite more of the surface of the gunpowder all at once than it normally would, which can create a pressure spike from the expanding gasses, instead of a fuller load causing less powder being ignited at the same time, and then combusting in a more controlled manner.

For a self-professed non-expert, it seems that you are quite knowledgeable. You have given the same theory as Big Cholla, but just in different words. I am no expert myself, but do know a thing or two about the rates of chemical reactions, and this idea sounds very plausible.

 

[WR Moore]

Back in the late 1960's I saw a revolver like the one described. I won't repeat the guys loading method. HP White tested the cartridges and found the pressures far exceeded proof loads. At this distance in time, I won't trust my memory as to the actual pressures.

Just to give a little perspective on this, a couple of years ago we had a rifle damaged by 5.56mm blanks. The cartridges were found to contain about 6 grains of a powder tentatively identified as HP38 (IIRC, producing about 7,000 to 12,000 psi). Cause of the damage was determined, by H.P. White, to be multiple powder charges. Now, if 6 grains of powder rattling around in a 5.56mm rifle case won't detonate, the chances of powder detonating in a pistol case don't exist.

BTW, the effects of powder charge position and surface area of the charge exposed to the primer flash were studied by H.P. White and found to be insufficient to cause catastrophic damage. On the other hand, damage as a result of double/triple charging is repeatable in experimentation. Occams razor suggests that someone stuffed multiple charges in the case.

 

[VAdoublegunner]

I've followed the several theories and only 2 seem to make sense to me. The "bullet as bore obstruction" sounds pretty good, where the primer force alone is enough to cause it to move forward and act as a obstruction in the forcing cone while the normal burning rate for the powder goes awry into high kinetics. But I agree with HP White that the actual chemical energy available in the powder is not likely enough to cause that sort of destruction.

The other is the pressure wave phenomena, where the low powder volume and primer flame flashover ignites both the primer end and bullet base end of the powder almost simultaneously, resulting in a constructive pressure wave that meets in the middle causing a constructive interference wave front possibly as much as 4 times normal pressure. Sort of an internal shape charge phenomena. That could result in more pressure than due to stored chemical energy alone.

But I still believe that most such incidents are due to loading errors, and if it is the second phenomenon it would have to be a very rare, and precise, unfortunate set of circumstances.

 

[Big Cholla]

I certainly agree with the concensus of opinion in that most 'kabooms' occur because of reloading errors, i.e. multiple charges of powder or a prior squib load leaving a lodged bullet in the bore for the resulting kaboom on a subsequent shot. With that said, multiple occurrences of overpressure detonations have been observed where the only explanation is as described by VAdoublegunner, nuubee and myself.

I have been reloading for 54 years. I have never experienced a kaboom. I have always avoided using fast burning rate powders in large capacity cases. My personal rule of thumb is to never use any powder that for my chosen load does not occupy at least 3/4 of case capacity. I never use Bullseye powder only for the reason that it is too easy with which to make a mistake. IMHO every shooter should be taught that if a shot does not sound right that the firearm MUST be opened and the bore examined for a squib load before the next shot. Most all primers develop enough pressure to send a bullet into the bore even with no powder present. Even factory loaded cartridges on occasion come without any powder or some other problem. Ray Chapman lost his second IPSC World Championship solely due to a factory loaded .45acp without a flash hole from primer pocket to powder.

.......... Big Cholla

 

[Pisgah]

Keep in mind that, as far as I have ever been able to determine, this phenomenon has NEVER been reproduced in a lab setting, even though it supposedly happens with fair frquency. What IS easily reproduced is the results of these supposed "undercharges", and that comes about, every time, from a double charge.

I am convinced that what happens is a reloader inadvertantly double-charges the case, and then ever after claims "it was only 2.5 gr. of Ol' Stump-Blow". A prime reason, IMO, to try to stick to loads too bulky to ever let a double charge go unnoticed.

 

[38-44HD45]

Will this myth never die? S.E.E. has only ever been (possibly) replicated in artillery ammunition. No one has ever been able to replicate "detonation" in small arms ammunition. In every well-investigated, documented case in which someone suspected that detonation caused a "kaboom," other causes have been found. Usually, it is either the wrong powder, like 40 grains of Bullseye in a .30-06, double or triple charges, or a bore obstruction. Here's the problem: A given charge of a given powder possesses a finite amount of energy. It takes a given amount of energy to rupture a barrel or cylinder. An undercharge of a powder that is otherwise an appropriate powder for the given cartridge simply does not have suffucient stored chemical energy to cause such a rupture, regardless of how fast it burns. And it does burn, not detonate. Other than the questionable artillery study, no one has ever gotten smokeless powder to detonate. Always investigate user error first!

 

[Scrapper]

I certainly agree with the concensus of opinion in that most 'kabooms' occur because of reloading errors, i.e. multiple charges of powder or a prior squib load leaving a lodged bullet in the bore for the resulting kaboom on a subsequent shot.

I have been reloading for 54 years. I have never experienced a kaboom. I have always avoided using fast burning rate powders in large capacity cases. My personal rule of thumb is to never use any powder that for my chosen load does not occupy at least 3/4 of case capacity. I never use Bullseye powder only for the reason that it is too easy with which to make a mistake. IMHO every shooter should be taught that if a shot does not sound right that the firearm MUST be opened and the bore examined for a squib load before the next shot. Most all primers develop enough pressure to send a bullet into the bore even with no powder present. Even factory loaded cartridges on occasion come without any powder or some other problem. Ray Chapman lost his second IPSC World Championship solely due to a factory loaded .45acp without a flash hole from primer pocket to powder.

.......... Big Cholla

I agree with Big Cholla. I have been Hand-loading for 40 years and my Dad and I always used slow burning powder which fills the case up most if not all the way without compressing it. (it usually works out this way when using Hornady's recommendations).

We stayed away from fast burning powders as much as possible for fear of a mistaken double charge. Besides we had much success with Hornady and others recommendations all those years.


Thanks to Hornady, Speer, Sierra, Nosler, Lee, Lyman and now Barnes I have more interesting things to try out and I'm sure I'm gonna have fun doing so.

 

[tops]

There is no way that a small amount of explosive can have a bigger explosion than a large amount of explosive. That is what I was taught in the first grade. Since then I have been to a goat roping and a county fair and haven't saw anyting to convince me otherwise. Larry

 

[Paul5388]

Finnish firearms expert P. T. Kekkonen wrote this concerning SEE:

Highest measured detonation pressure was 10 000 atmospheres. A pietzo-electric pressure gauge was broken and highest grade on the pressure scale was this 10 kilobars. A sturdy test-barrel of a German gun-proofing laboratory was wrecked, of course.

This disastrous test was repeated with another set of equipment for the sake of comparison. Pressures of first shots were slightly less than normal. It might be fifth or sixth shot, when the new test-shooting barrel blew up. Again a pressure gauge disintegrated and a scale told: 10 000 atmospheres! It was presumably just a fraction from whole horrible truth, because so called "wave pressure" of a detonation may exceed reading A HUNDRED THOUSAND ATMOSPHERES, when the explosive material is in gaseous form of existence, pre-heated and pressurized before explosion.

Caliber of tested cartridge was .243 Winchester, bullet weight 80 grains, powder then-new NORMA MRP, and the charge... surprisingly... just 15 % less than a maximum (compressed !) load. It was STILL A REDUCED CHARGE DETONATION; not one caused by an excessive charge, because the charge could not be excessive with those components in use. Light bullet and slowly burning powder is not an advisable combination of loading components for .243 Win., known as a caliber prone to S.E. Effect. (It's "big brother" .308 and "kid brother" .22-250 are considerably less risky; last mentioned presumably because of more steep 25 degrees shoulder angle).

He also alluded to the formation of combustible gases that ignite suddenly as a probable cause for very low density loads detonating. In that case, he was referring to a 3.0 gr load in .308 Win, which is going to be hard to duplicate in a handgun and is certainly not comparable to the cited 2.7 gr of Bullseye in a .38 Special.

So, I would vote for a 5.4 gr or 8.1 gr load blowing the OP example gun up.