How do Revolvers Kaboom?

R

RougeLeader

Inactive
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.
 
Typically, in a revolver, the cause is a double charge of powder which will blow the frame and cylinder, sending shrapnel pieces everywhere.
 
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.
 
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?
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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
 
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.
 
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, 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.
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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
 
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
 
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.
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Head scratch. Seems a bit like we would die without breathing?
 
cecILL wrote:
The case just holds the propellant. It would explode without the cylinder/chamber.
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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.
 
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Bad things happen sometimes...........
 
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.
 
hdwhit said:
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.
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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.
 
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.
 
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....
 
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.
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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
 
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.
 
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.
 
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