The authority on pistol and rifle loading data since 1996.

Light loads in large cases can explode (2007 update)

There has been much said about a chance of a gun blowing up with very light loads (usually of fast burning powders) in big cases.

On the other hand, a much more common reason for an explosion is a double charge that can happen VERY easily with small charges in large cases. An excellent article discusses this as the most probable cause of many blow-ups. See “When Bad Things Happen To Good Guns” in the November 1996 edition of “GUNS” Magazine by Charles E. Petty. (p. 43)

Here are several opinions. The first is from an internet mail message I read, and have paraphrased because the author did not want his name used on the comments. The second is from Charles J. Sharps Ph.D., whose Thompson Contender with a 45-70 barrel blew up. Next is an opinion from the “Cowboy Action Shooting” e-mail pages. The last opinion discusses SEE (Secondary Explosion Effect).

Re: The Light Load Controversy

People seem to be familiar with light load ruptures, but they are very difficult to reproduce. It lends some to believe it was from a double-charge accidently put into the case, but it does have references going back to the 1881 period of time.

There is some agreement on the following: Very low density loads (meaning the ratio of powder volume to cartridge case volume) of very fast powders under varying environmental conditions can create up to 4X normal chamber pressures and may cause the light load rupture to occur. Ruptured barrels can be symptomatic of too much powder (double charge loads, etc.). Ruptured cylinders and dissappearing backstraps can be sypmptomatic of a light-load rupture.

The use of low density charges with one of the top 10 fastest powders in the world at half the recommended factory charge weight may work in your gun, but it’s risky.

It may not work in someone else’s gun. Therefore, no one should recommend very light loads, especially of fast burning powders to anyone. Stuck bullets is another matter. With very light loads and powder against the bullet, a very mild shot can stick a bullet in the barrel. The NEXT shot can have disasterous consequences, also leading to the cautions against very light loads of any type, but especially of fast burning powders at the other end of the case from the primer.

There has been an article published in Trails End Magazine on this same subject (see Volume 1, No. 3 Oct/Nov 1995).

From: “Charles J. Sharps Ph.D”

Date: Wed, 25 Sep 1996

March 14, 1993

by Charles J. Sharps Ph.D.

Websters defines debacle as a breakup, or a sudden great disaster. Yesterday, detonation, secondary explosions, or just plain stupid reloading, signaled the breakup of my once beautiful SSK 475 JD Jones. As Webster writes, “it was a disaster.”

In my last story about the .475 I remarked on its being just plain brutal to shoot. So I went searching for less powerful loads that I could enjoy plinking with.

Reading everything I could find about 45-70 (not an error) for loads which might be used in the larger .475, I decided I would try some 300 grain Barnes jacketed round noses and some IMR 3031 which is considered safe in a trapdoor Springfield.

I ordered my bullets from some outfitter in Rhode Island, waited the usual nine days for UPS to deliver here in Oregon and sat down to reload. The 475 JD Jones uses 45-70 brass that is blown out into a straight case in order to utilize the .475 diameter bullets. There are two ways to fireform the 45-70 so that it fits the chamber of the .475. One way is to run the case up over the decapping rod far enough to seat a .475 bullet, use a mild load, and fire, but it is not very effective.

The problem with this, is the case mouths are apt to come out longer on one side than the other, needing to be trimmed, requiring yet another step in the reloading process.

The second way is to actually fireform. Looking around my reloading room I spied the thousands of rounds of 500 grain cast bullets in .458 diameter that have been cluttering up a corner, ever since I quit shooting cast bullets in my .450 Ackley Ruger Number 1.

My idea was to load the 45-70 cases with a mild load of 2400, recommended in the Lyman Manual for trapdoor Springfield’s, use the way undersized bullets to develop just enough pressure to fireform the cases and they should come out perfectly.

No case mouths would need to squared or trimmed, thus eliminating another reloading step. Remember, I was looking for the easy way out. I was also being a bit of a tightwad, I did not want to send fancy (read as expensive) Barnes bullets I had just purchased, crashing downrange, just for fireforming, nor did I want to use my limited supply of .475 cast bullets.

I have lead by the hundred weight and a .458 mold, what could be easier? I decided to load ten rounds. I dumped the powder into my hopper, set the scales, used Federal 215 large rifle magnum primers and the already mentioned bullets, and proceeded to reload. It was while I was filling the cases, that I had this niggling thought, that I should be using some dacron or over the powder wad. The niggling thought was, somewhere, I had read that small amounts of 2400 when used in cases with large volumes can be extremely explosive.

But not this load after all it is recommended for Trapdoor Springfield’s and they are not considered to be the worlds strongest actions.

Carefully reloading my ten cases I went out with my son, brother-in-law and hunting partner to fireform my cases and to do some general plinking. Arriving at our shooting spot I took aim at aclay pigeon set up in the sand about 10 yards away. I was going to try and hit it with a .458 bullet traveling down a .475 bore. My first three shots were close but the pigeon remained unbroken.

Examing the cases I was pleased to see my first three shots yielded three perfect cases. Just as I was set to fire my fourth round Jack hollered asking a question. Pointing the barrel straight down while releasing the hammer I turned to answer. I then raised my Contender and just knew that this time I was going to bust the pigeon.

Pulling the trigger my Contender exploded. Reeling and dazed by the violent explosion, I just stood there stupidly looking at what was left.

Swearing, not really understanding what had happened, I could see my barrel lodged into the ground just ahead of my feet. I tore my headphones of my ringing ears and yelled, “I just blew up my blankety-blank gun.”

Jack Fearell, my brother-in-law and fellow Contender aficionado standing almost 100 yards to my rear said, “are you all right?” and came running. About that time there was a clink as the back half of my Leupold scope hit the ground near him. Neither one of us knew at the time what it was but it made such a distinctive sound Jack said, “What was that?”

We later discovered the scope piece and you can figure out how high it must have gone into the air before returning to earth.. Settling down, I started to take stock of what I had. The barrel, with its underlug missing, was at my feet. Its’ breech a gaping maw of three fingers of bent and twisted Shilen steel. The 4x Leupold scope and TSOB were gone. The Pachmayr forend was still attached to the barrel and in my hand was the Contender frame, minus one side plate and the other badly distorted.

Jack came running, again asking, are you okay? Another shooting partner, Orvel Bird checked out my hand and said, “what do you think happened, a double load of powder, a lodged bullet or what?” No, I thought, I saw the last bullet hit the ground and I checked all the cases after charging, it must have been detonation.

Detonation is defined as a violent explosion caused by the powder igniting instantly or all at once, creating tremendous pressures. Remember all smokeless powders are designed to burn at a controlled rate. Looking at the barrel lying on the ground, I could tell there was something wrong with it but did not know what. Jack asked, “where is the scope and TSOB?” Realizing what was wrong with the barrel, the scope was missing. I, still in shock said, “well maybe we can find it and it will be okay.”

The reality of what had happened, was starting to sink in. My entire Contender was destroyed. Not damaged, but destroyed. I was probably the luckiest man alive, I had my hand(s) my head, my eyes, everything. Lucky in many ways. For instance, for accuracy, I usually shoot two handed, sometimes with my left hand on the forend, today it was different. I had just wanted to bang off ten rounds to get them fireformed and all I was doing was shooting dirt and a clay pigeon, one handed.

Jack went back down the road where he and Orvel had heard something clink and found the back half of my scope. It looked like it had been run over by a tank. It was no longer round but flattened, but the eye glass was not broken. The TSOB had been torn in half with one ring still attached.

Orvel, after examining the barrel and as a retired engineer figured that the front half had to have gone an equal distance to the front. It had. Jack found it after just a few minutes of looking. The rings had held, the scope and TSOB had been ripped into two, but the front bell was still attached.

Remorse, started flooding my mind, what had I done to destroy a beautiful barrel and frame? Not only had it been owned by Joe Wright of TCA fame, but it was marked, barrel number two. Dollar signs kept flinging themselves about, as I loudly tallied up how much money I had invested and subsequently lost.

Orvel brought things back into proper perspective when he again reminded me I was not hurt, and that fingers, hands, and eyes are priceless.

We spent another half hour or so looking for missing parts. I found the 45-70 case, it had been ripped wide open and laid flat in the dirt. It had been a new nickeled case and powder discoloration demonstrated it had not been overloaded.

The barrel lug which had also been blown off was found complete with hinge pin and the pin moved easily. The missing side plate was not far away.

Examining the barrel and frame, I think what saved me from injury was the entire explosion went up, down, and sideways. There is nothing to demonstrate that it blew backward. The primer is still tight in the case and the case head shows no signs of pressure. The frame will still cock, and the trigger works, a tribute to the strength of Warren Center’s design. With the exception of the scope, all missing parts were found within three feet to the front and sides of my feet.

My hand was starting to hurt and it was time to return home, where the first thing I did was pull and weigh all the remaining cartridges. Nothing was overloaded.

Sitting around later trying to figure out what I had done wrong, but still suspecting detonation, I decided I would call J. D. Jones of SSK Industries and ask what he thought had happened.

Calling JD, I told him this story and he said, “Fast burning pistol powder, when put into a large case with lots of air will detonate. I can’t prove it, but I have heard too many stories like yours for it not to be true. Your pointing it at the ground just before firing probably put all the powder up against the bullet.”

Talking with JD for quite some time put my mind at rest as to what had happened, but I was still at fault for not following my conscience.

I knew from years of reading and reloading that mixing 2400 with large cases was not the intelligent thing to do. You can and will find this particular combination of powder and cases in two of today’s current reloading manuals, (Lyman and Sierra). Before you use them, I suggest you remember this story.

Remember the niggling I had in the back of my head at the beginning of this story? I should have listened. If I had, I would not be without my handloaders.

NEVER, NEVER, mix fast burning pistol powders like 2400 with large volume cases without some sort of overpowder wad, for if you do, you too could experience a debacle.

Charles J. Sharps Ph.D.

Here is another comment recently downloaded from CAS-City pages.

Date: Sun, 29 Dec 1996 12:22:51

From: One Horse

Subject: Re: Detonations

This is an important thread because the more people try to use popcorn poppers { light loads} the more chance there is for more destructive events. Far be it for me to argue with FBI Ballistics but as a Ph.D. chemist with more than the average knowledge of explosives and such:

  1. There are studies that show that essentially all the powder in a typical pistol load combusts before the bullet leaps the gap into the forcing cone.
  2. The expansion that occurs is the expansion of the gases produced in the combustion not the expansion of the powder.

The best argument for why detonation occurs rather than the simple burning and slow burning rate of smokeless propellant is that very light loads expose a larger surface to the primer jet, By analogy, granary explosions occur when finely divided dust is suspended in air-the effect is a detonation. If you have never seen a granary but saw “Outbreak”, the sterilizing bomb in the beginning of the movie is a fuel aerosol bomb { once called Daisy Cutter}. The rapid combustion/explosion/detonation is the result of the high surface area of the aerosol fuel droplets {total area of all the droplets}. The effct is dramatic and large landing zones for helos can be created where no stumps are left but no crater is formed. The analogy is to a the high surface area of a flake or ball powder expose to ignition if it is spread as a thin layer over an entire case length. More powder gets burning sooner and ….

One way to make a lab experiment fail is to load and keep the cartridges bullet up and then load so as to not spread the light charge over the length of the case? If the theory is correct, that is. There is a pertinent article in the last issue of The Cast Bullet – the Cast Bullet Association journal.

Another view on the matter. SEE?

From: “Norman Johnson”

Dear Sir:

I believe that your article warning of the dangers of SEE has inacuracies that will discourage some shooters from safe and satisfactory experimentation.

SEE is an unexplained pressure excursion which has often blown up guns. It is associated with markedly reduced loads of very slow powders.

Contrary to the ubiquitous old wives tale, detonation is NOT a consideration with fast powders such as Bullseye, no matter how light the charge is or how spacious the case.

The phenomena of Secondary Explosion Effect (SEE) is known to occur only with the slow powders at very low loading densities. Precious little is known about the mechanics of the phenomenon and it is not even known if the expression, Secondary Explosion Effect, is accurate. SEE, despite best efforts of the leading powder companies, cannot be reproduced in the lab, at least in the literature that I have been able to find. Some of the powder companies now are putting notations in their manuals not to reduce CERTAIN loads below 80% loading density. One should note that such notations are for a very limited number of powders and cartridges, such as W-W 296 in the .44 Magnum. Actual documented SEE cases were at densities much less than 80% and with slow powders.

Cast bullet shooters discovered SEE while experimenting with some of the very slow powders. However, they have been using moderate speed powders at much reduced loads since the days of Dr. Mann, with no untoward results. Only the very slow powders exhibit SEE, usually those that were developed for the .50 BMG and magnum rifles such as MR-8700, etc. Recent events posted by Charlie Sharps, “Charles J. Sharps Ph.D” indicates that any powder that is SLOW FOR THAT PARTICULAR APPLICATION, loaded to a significantly reduced powder density, might be suspect. His was a Hercules 2400, .45-70 Contender blowup.

If SEE were a real danger with other than very slow powders, we would have MANY gun blow-ups. Think about it a minute. The .38 Special case uses only about 20 – 30% of its case volume when loaded with typical target loads. Anyone seen a .38 go high order from a (true) target load? Cast bullet shooters fire millions of rounds each year using VERY low loading densities in most cases.

If that is not enough, the ultra-lite loads have been experimented with for a good many years, where a typical powder charge might be 2-3 grains of Bullseye, 700X, Unique, or any faster pistol powder in a .30-06 or .45-70 case. If SEE were a realizable phenomena for fast powders at greatly reduced loading densities, this would certainly have resulted in many blow-ups. These ultra-lite loads are not isolated uses as the NRA has written them of them over the years, at least as far back as 1967 (NRA Handloaders Guide, Pg. 154). Reloaders, unfortunately, ascribe some anomalies to conditions other than the actual causes. Several other things that can happen to increase pressures:

  1. Excessively thick case neck thickness due to reforming procedures or metal flow – causes over-diameter cartridge neck. Jamming the large cartridge neck into a tight chamber neck is a very good recipe for disaster.
  2. Build-up of residue in the neck area of the chamber which compounds 1, above. Cast bullet shooters have experienced this from lube build-up.
  3. Stretching of case length resulting from both firing and drawing the expander button back thorough the neck during resizing – causes the mouth of the case to jam into the corresponding chamber area and impede bullet release.
  4. Significant increase in local ambient temperature over that in which the load was developed. This can have more effect than the unwary may suspect.
  5. Changing to another lot or manufacturer of brass that has a smaller internal volume. This is usually a hazard only if maximum loads for the gun were developed using larger internal volume brass.
  6. Bullet seated to a greater overall length (OAL) so that bullet is forced into rifling when the action is closed. This is, of itself, not a hazard; many of my cartridges are prepared using this technique. However, if the load was developed with the bullet seated to normal factory load OAL, that same powder charge can be excessive when the bullet is seated so that it touches the lands.
  7. A change of bullet ogive so that the effect of 6 is realized even though cartridge OAL remains the same. I have found at least two boxes of .22 caliber bullets that had noticeably different ogives in the same box.
  8. Change to another lot of powder that is faster albeit of the same manufacturer and type.
  9. Excessive headspace (or too short cartridges) which can result in head separation and allow hot gasses and molten metal to blow back in the shooter’s face. This is not necessarily a pressure excursion, but that is often blamed as the problem.
  10. Excessive powder charge. Reloaders are usually not willing to admit this possibility, but we all make mistakes. About 100 years ago, on the second box of .38 Specials that I ever loaded, the charges were so excessive that the web my poor wife’s hand was split open. The gun held together and so has our marriage (five kids).

Of these causes, I have found numbers 3 and 10 to be the most common cause of pressure excursions.

SEE is a very real phenomena, but it is blamed many times when the shooter has, in fact, allowed one or more of the above conditions to occur. For those who care to investigate further, back issues of The Cast Bullet have a number of articles discussing same. Handloader has also treated the subject a few times.

SEE is a real phenomena, but, I suspect, not as prevalent as rumors would indicate.


(Comment on gun blowing up from reader. Date: 9-26-2007)

Hello Mr. Smith

I was reading your site, very nice I must say and full of good info, and came across something in you “FAQ’s: And Answers from my e-mail pages (1-14) 1996” section. Here you said it was ok to use 38 spl loads in a 357. I thought I would share with you something that happened to a friend of mine while I was standing next to him on the firing line.

He had new Star progressive reloading press. He wanted to use this fine contraption but didn’t want to load for 357 so as to reduce recoil. He had been using 38 spl light loads. So he used this same loading in the 357 brass. I was standing next to him and heard a strange sounding report of the pistol. And his bullet strike was about four feet in front of us in the dirt. He is a very good shooter and I wondered why he had hit the dirt. I turned to look at him. His face was as white as a sheet. The top strap of his pistol was gone and the frame was bent so that the barrel was pointing at the ground in front of his. His 357 had detonated!

Some ballistic labs claim this can’t happen. Well I’m here to tell you that it can and does. We jawed about this for a long time and the only thing that came up that made any sense to me was this theory. With the light 38 spl load in the 357 case there was not enough powder to fill the case half full. This caused it to be spread across the side of the case while in the chamber and below the flash hole of the primer. When the primer fired flame from the primer ignited both ends of the powder. This caused two flame fronts inside the case. When they met in the middle of the case the pressure went way up and destroyed the pistol. It was put forth that he had accidentally thrown a double charge. But with the star reloading press this is not possible. It is possible to throw a no charge or a light charge if the powder measure is clogged but not a double charge.

I though I would share this with you so you can warn others about using light 38 spl loads in the 357 brass.

Thank you for your time

Joseph Murphy

(My Reply to this email)

Yes, I certainly can believe it happened. I is OK to use .357 cases, but not with light loads. There is a strong warning about light loads that can explode on the first page and top paragraph of my web site . . . and that’s light loads in regular cases. Certainly you’d think someone would know that light loads in an even larger case could be a problem. Using a light load with a low density powder that would be light in a .38 case, is a very, very bad idea in a .357 case. Your theory as to what actually happens inside the case is as valid as any others I have heard for when this event occurs.

Yes, sometimes a double charge can do the same thing. And, with very light loads, a bullet can get lodged in the barrel and the next shot will blow up the gun. So that’s two things in addition to the “light loads explosion” that can happen. Case position of the powder with light loads is another issue. I have found (read my web site about powder position in cases) that velocities can vary tremendously with a small amount of powder in cases that were tilted forward or backwards before firing, so that the powder was full against the primer or the lead bullet.

Thanks for writing. Sorry your friend had to find out the hard way about small amounts of powder in large cases. I will share this with others.



MD Smith

MD Smith

MD Smith has had a storied career from his family broadcasting AM radio business, to his 36 year career in TV broadcasting. He is a published fiction and non-fiction writer, earned his pilots license in 1965, and is the original founder of Reload Ammo in 1996. His loads have been successfully tested and used by others for more than 25 years.

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