How do Revolvers Kaboom?

[RougeLeader]

Hello everyone! I've been working up a 38 Special load based on my 44th edition Lyman manual (10.7gn 2400 topped by a 158 LSWC) and have been warned multiple times to be careful.

In doing my research ahead of time, I found many warnings of firearm failures, or Kabooms, but I didn't find many details of how exactly they would fail. I also found warnings that the old stout loads and 38/44 loads were designed for N Frames and other revolvers of similar cylinder size.

My question is how exactly revolvers fail when you push things too far with powder. I understand a double charge can certainly burst the case and the cylinder, but even a 357 load doesn't really seem to deform the case itself to any significant degree, much less stress the cylinder around the case. Is it the freebore portion of the the cylinder directly after the case mouth that fails? Is it the frame itself that fails under the force of the cartridge being fired?

Before anyone gets concerned, I'm not intending to blow anything up. I'm a grad student in a combustion engineering lab at the University of Connecticut (yes I know, please be kind) and am well aware of the dangers of explosives of any kind. The load I'm working with is safe, and I already have ~500 fired out of a K Frame. I'm merely curious from a theoretical standpoint.

[FITASC]

Typically, in a revolver, the cause is a double charge of powder which will blow the frame and cylinder, sending shrapnel pieces everywhere.

[cecILL]

The case just holds the propellant. It would explode without the cylinder/chamber.

[RougeLeader]

FITASC, thats about what I figured. Nasty stuff, reasons why I check every drop. I'm a terrible shot with 10 fingers, don't want to try with less!

cecILL, I understand that. I wasn't precise, that was my mistake. What I meant was that even in extreme powder loadings (attempted with 357 rated guns) the brass does not seem to deform to any significant degree after firing when compared to a mild load. Shouldn't the case either experience plastic deformation and establish a friction bond with the cylinder itself and/or rupture completely before the cylinder or frame fails?

Not arguing with you guys, again just curious.

[USSR]

My question is how exactly revolvers fail when you push things too far with powder. I understand a double charge can certainly burst the case and the cylinder, but even a 357 load doesn't really seem to deform the case itself to any significant degree, much less stress the cylinder around the case. Is it the freebore portion of the the cylinder directly after the case mouth that fails? Is it the frame itself that fails under the force of the cartridge being fired?

The cylinder will fail long before the frame. BTW, your load is perfectly safe in your K frame; Lyman lists a maximum of 11.0gr and was tested in a Model 14. I can only surmise that the warnings to be careful are related to using your powder measure. Personally, I would set my powder measure to drop a few tenths of a grain light and trickle up to that charge weight.

Don

[reddog81]

With an extreme over-pressure event the cylinder will give out and may take the top strap with it. You can also run into bulged cylinders that are mildly deformed from loads that were way too heavy but not stout enough to cause a rupture.

Brass is pretty elastic and is the top choice for cartridges because of this feature. Every time you shoot the brass should expand to to fill the chamber and prevent blow back and then once the bullet leaves the barrel and the pressure drops the case should bounce back a little and release from the cylinder with ease. one way reloaders watch out for over pressure loads is to take note once the extraction of brass begins to get difficult. Once you start to approach the pressure threshold for a gun the cylinder also starts to expand and contract under pressure. When this happens the brass from the case and steel from the cylinder do not expand and contract at the same rate and the steel from the cylinder grabs onto the brass making extraction difficult. The thinnest part of the cylinder is typically were the notches are and the area around there is typically the first to give out.

Conversely, reloaders should watch out for scorched cases because this means the brass is not experiencing enough pressure to seal off at the case mouth.

[RougeLeader]

Thank you for the complete answers guys.

reddog I had forgotten about how much strain it actually takes to permanently deform brass. No one ever said we students were always smart! Thanks for the tip regarding the scortched brass. I had not heard of that!

USSR, that 11 grain limit is exactly what my Lyman manual says and I've even shown it to people here in CT, but evidently they still believe that the load is very dangerous. 3 different people have told me in person that I shouldn't trust data previous to ~1990. No idea why. I do trickle charge like you suggested though.

[USSR]

USSR, that 11 grain limit is exactly what my Lyman manual says and I've even shown it to people here in CT, but evidently they still believe that the load is very dangerous. 3 different people have told me in person that I shouldn't trust data previous to ~1990. No idea why. I do trickle charge like you suggested though.

The reason, no doubt, is a single word: 2400. 2400 powder is typically used with magnum handguns, and they don't realize that it can be used in moderate quantities in nonmagnum handguns.

Don

[F. Guffey]

Based on my experience on the Internet there is no fix; for me there is nothing entertaining about pulling the trigger without a clue as to what is about to happen.

there was a foreign company that started out to answer your question; problem, what do those foreigners know. As soon as the information got over here reloaders thought they were talking about an internal combustion engine.

Preignition, detonation, powder that did not have the ability to prevent knock and the timing was set to ignite to early.

The foreign company said it will not happen ever time, and then went on with their business. Here? We demanded it happen every time so we occasionally blow up a pistol and claim "it must have been a double charge"

My first progressive press was outfitted with a powder lock out die for straight wall cases and a powder die for bottle neck cases. I also weight the components, when finished I know the gross weight of the round because that is the last chance I have to eliminate the possibility I have to eliminate the possibility of blowing rendering one of my pistols scrap.

F. Guffey

[RC20]

Pretty tough to figure out a weight variation in a pistol case due to an overload. Not much in there and components vary but then if you weighed all the stuff before hand and sort into discrete groups you might see it. Maybe.

The case just holds the propellant. It would explode without the cylinder/chamber.

Head scratch. Seems a bit like we would die without breathing?

[hdwhit]

cecILL wrote:
The case just holds the propellant. It would explode without the cylinder/chamber.

Actually, it would not.

Ignite the primer in an unsupported case and once the pressure inside the case reaches the level to overcome the friction between the bullet and the case wall (which, ignoring some effects of dynamic friction, is the same pressure required to seat the bullet in the first place so you know it's not very high), the bullet would pop out and relieve the pressure.

To get an unsupported case to explode, you have to restrain the bullet's movement when you ignite the primer.

[FITASC]

Bad things happen sometimes...........

[Metal god]

I think what's best to know is not how a revolver blows up but why a firearm can blow up. To say a double-charge, although accurate, is too simplistic. My guess is just as many blow-ups happen using the wrong powder as do with double charges.

I wish I still had Unclenick's explanation on this subject still copied so I can post it. Maybe he'll come by and clean up what I'm about to say.

It's really about the burn rate of the powder or speed in which the gases expand and the ability of the bullet to outrun those expanding gases. This is why you hear about rifles blowing up when someone mistakenly uses a pistol powder in a rifle cartridge. Pistol powders in general burn much faster than rifle powders (gases expand much faster). So when you use a much faster burning powder than a cartridge is designed for, the bullet cannot move down the barrel fast enough to allow room for the ever-expanding gases. Those gases are going to keep expanding regardless, and if the bullet can't get out of the way (basically plugging the barrel) you get the KABOOM.

This can also happen when using the correct-for-cartridge powders (right powder burn rates) but too-heavy-for-caliber-bullet to push down the barrel fast enough to stay ahead of the expanding gases. As you will notice in your manuals, as the bullet weight goes up in a given cartridge the charge of a given powder goes down. This is true throughout the available bullet weights for that cartridge. This is because of basic physics, which is at least two-fold and likely many more, but I'll stick to the two basics.

To increase bullet weight the bullet must get longer. The reason is simple: the diameter is fixed because of the bore diameter of the given cartridge you are shooting is fixed. When the bullet gets longer the bearing surface that makes contact with the bore (drags along the bore also increases. This increased drag results in the bullet being harder to push down the bore, slowing its ability to outrun those expanding gases.

The other is the simple fact that with all other things being equal, a heavier object is harder to move than a lighter one. This again slows the bullet resulting in its inability to outrun the expanding gases.

Generally speaking, this is why when you see, in a given cartridge, some powders are listed for the light bullets but are nowhere to be found in the heavier bullet data. Some powder burn rates are just not suitable for certain bullet weights in a given cartridge. This also works in reverse, as slower burning powders don't work well when using light-for-caliber bullets but for a different reason. Someone else can speak on that if the OP wants.

[reddog81]

Originally Posted by hdwhit

Actually, it would not.

Ignite the primer in an unsupported case and once the pressure inside the case reaches the level to overcome the friction between the bullet and the case wall (which, ignoring some effects of dynamic friction, is the same pressure required to seat the bullet in the first place so you know it's not very high), the bullet would pop out and relieve the pressure.

To get an unsupported case to explode, you have to restrain the bullet's movement when you ignite the primer.

Your statements sound logical however, there are plenty of online videos showing live rounds going off outside a chamber and the brass case get mangled and sends shrapnel flying.

[Metal god]

To get an unsupported case to explode, you have to restrain the bullet's movement when you ignite the primer.

Like a heavy crimp ???? Things that make you go hmmm

[RougeLeader]

I would think that it would be powder, case, and load dependent. The projectile should exit the case at extremely low pressures, this is easily confirmed, however there will be a given timescale for this to happen. Should pressure build beyond the ultimate stress of the case before that time elapsed then the case would rupture. If not, then the projectile would exit the case and relieve the pressure.

We see this in our lab experiments all the time. Chemical vs physical timescales produce interesting results.

These are just my thoughts though.

[RougeLeader]

If anyone has a high-speed camera and some unwanted powder/cases this would be easily tested. Otherwise I could try to 'borrow' one from the lab....

[F. Guffey]

Pretty tough to figure out a weight variation in a pistol case due to an overload. Not much in there and components vary but then if you weighed all the stuff before hand and sort into discrete groups you might see it. Maybe.

I am surrounded with reloaders that cannot do it. And then there was the reloader at the firing range: he had locked up his pistol without powder in the case, We removed the bullet by driving it back into the case. After we cleared his pistol he began loading 6 more rounds.

I stopped him and then reminded him he chambered a round with no powder. I wanted to know how he knew the next round he chambered did not have twice the necessary powder. We offered him all the ammo he could shoot. We offered to help him with his reloading. I could not convince him that, with discipline, he could weigh his rounds to determine if all the cases had the same amount of powder. He claimed that could not be done, I offered to loan him a scale, etc.

He left the range mad. We tried to explain to him the danger he exposed us to by not knowing if his pistol was going to scatter, lock up or shoot.

I was impressed because he did all of his reloading on a RL550B.

F. Guffey

[RougeLeader]

I'll be honest here, I actually have found powderless loads that I accidentally made by simply weighing them. When in doubt, thats my check. If still in doubt, take them apart.

F. Guffey, are you using that method as a double check for the load itself as well?

The thread kinda diverged a little. If thats my mistake I'm sorry, I'm new here.

[reddog81]

It's certainly possible to determine if a load is short the powder, assuming the brass is all from the same lot and fairly consistent in weight. Trying to find a round with missing powder among cases with mixed headstamps and different lots of brass is going to be much more difficult and at that point you'd be better off pulling down all the rounds.

[FITASC]

Easier to do with large capacity rifle rounds than handgun rounds..........

[F. Guffey]

It's really about the burn rate of the powder or speed in which the gases expand and the ability of the bullet to outrun those expanding gases. This is why you hear about rifles blowing up when someone mistakenly uses a pistol powder in a rifle cartridge. Pistol powders in general burn much faster than rifle powders (gases expand much faster). So when you use a much faster burning powder than a cartridge is designed for, the bullet cannot move down the barrel fast enough to allow room for the ever-expanding gases. Those gases are going to keep expanding regardless, and if the bullet can't get out of the way (basically plugging the barrel) you get the KABOOM.

Again, the shooter standing next to me locked up his Model 66 when he pulled the trigger on a round with no powder. Because time is not a factor to most reloaders there is no reason to waste my time explaining what could have happened had the bullet made it past the forcing cone and then stopped in the barrel.

And then there is the other time factor, the primer is fast, with a slow burning powder the primer can plug the barrel with the bullet. With the plugged barrel there is a chance the bullet can not move out of the way fast enough and I would guess the pistol would then be rendered scrap.

I am the fan of the jump start, I want my bullets to hit the rifling 'a-running'. I am not entertained by the ideal the bullet could have a difficult time getting started.

F. Guffey

[HiBC]

I have no data to back this up,so it is opinion.

I suggest we discern between catastrophic blow ups,and just ruining the gun.

There also,at least in theory,isolated anomalities. For this I mean something like a flash over detonation. These may be "I can't prove it did or did not happen,but I don't believe I used the wrong powder,etc"

Actually blowing up the gun is seldom about pushing the max load,or the max load plus a little.
If a powder measure is functioning properly,the one or two or three tenth grain variation is not going to blow up a gun.

If we are starting with a sound,undamaged gun,not in any particular order:

Using the wrong powder

A double or triple load

A bore obstruction.I would include a mis-indexed cylinder here,and a no-powder squib load leaving a bullet in the bore

In some cases,maybe defective brass failure.This would more often be in a semi-auto.

I am NOT saying pushing the max or max + will cause no problem. A cylinder can stretch or swell a bit before it blows. This may show up as hard extraction.

Frame scan stretch,end play increases,cranes become misaligned,top straps can gas cut....
Pushing or exceeding limits can turn a fine handgun to junk in short order.

But to blow it up... It may be Bullseye was accidently used instead of 2400.

SO...only one powder on the bench,read the recipe for the load,read the label on the powder canister,twice. Out loud is best. Use original,labeled containers(maintain traceability)
OOPS!Powder measure is half full from last time! I dump it on the lawn. That hurts!. Incentive to not leave powder in the hopper.

Avoiding squibs and double charges: I get it that some powders are attractive because they are economical.Bullseye is an example. Low dosage powder. Its a good powder,but I prefer to sacrifice some economy for load density.I prefer a bulky enough charge that a double charge is impossible or at least very noticeable.

For a manual press,visual powder level inspection before seating. For progressive presses,a powder cop die or some other failsafe is good.

The most common bore obstruction is a squib. If you drop a hammer without a boom and recoil,stop. Make sure the bore is clear.Captain obvious says "Don't look in the muzzle".A pencil can work.

With those precautions,you are not likely to blow one up.

If we load to 90%or 95%,our guns will last longer than if we load to 100% or 105% of max.(And nothing wrong with 70%)

And lets not forget,not all guns are equal. While a Charter Arms Bulldog 44 spl is a perfectly good gun,you might scatter one shooting loads that an N-frame S+W or a Ruger Blackhawk can handle. Cylinder wall thickness nan get quite thin,especially at the cylinder bolt latch notches.

[243winxb]

Revolver cylinders expand at each firing. Metal becomes stressed, then fails.

The PSI would have to be above normal levels for many firings, 10,000 rounds or more.

Most kaboom are a double charge of powder.

Thats my guess.

[Unclenick]

RougeLeader,

Brass is more plastic (malleable) and less elastic than steel. When a charge gets high enough, cases can resist ejection because the steel has expanded beyond the yield point of the brass but not beyond its own yield point, so it has then returned to its own original shape afterward, thereby clamping the expanded, less elastic brass in place. Many of the old-timers depended on this for revolver load development (read anything by Elmer Keith on load development). They would load up to the point the cases began to resist ejection, then back the charge weight down 5%.

The above is unique to revolvers because mushroomed and flattened primers and other pressure signs often fail to appear in revolvers before sticky ejection does. the steel is thinner at some parts of the chamber than others, so resistance to ejection is treated as a revolver pressure sign and therefore an indication you should back down. If you do not, but instead keep increasing the charge weight, the steel will give way first where it is thinnest, as FITASC's photos showed.

The reasons old load data are suspect are several. First, many old manual authors did not use pressure testing at all, instead of looking for pressure signs in a particular production firearm whose chamber(s) might be looser than others, and therefore needing more powder to reach a pressure sign. Moreover, pressure signs on a case usually tell you more about what the case can tolerate than what the gun can tolerate, the stick ejection being an exception. Second, manufacturers of and formulations for powders can and do change over time. An attempt is made to keep a new powder compatible with the original, but that may not always be exact. Almost all primer formulations have changed in some measure since 1989, and primers can have some effect on pressure. Many cartridge cases have at least slightly different capacities than they did even a decade ago due to outsourcing and changes in plants and tooling, forcing loads to be worked up again. Pressure measuring has advanced immensely since old data was developed, and now, instead of just a peak value, the whole pressure curve is revealed and in some instances, this has resulted in anomalies being identified that has changed load data. Probably the most notable was the warning from Alliant issued July 25, 2008, to stop loading Blue Dot powder in .357 Magnum with 125 grain bullets and to stop loading it in the .41 Remington Magnum at all. Old load data often has these loads Alliant says can be hazardous.

You are right about the time frame of firing events. Years ago, H.P. White Laboratories found they could not detect movement in a bullet before pressure reached 10,000 psi, despite bullet pull being only tens of pounds. That high number was due to the dynamics of the event. In the quarter millisecond or so it takes to go from primer pressure to 10,000 psi, the inertia of the bullet plays a significant roll in limiting its acceleration. Yet, if you fire just a primer with no powder, you can unseat a bullet into the throat of the gun. It's just that it doesn't happen as quickly. Given enough time, everything equilibrates toward steady-state behavior.