617-6 .22 Kaboom

[Delos]

The bullet beside the fired one was loose

Let me make my last entry a bit more clear.

For a flashover to occur the hot gasses or a powder trail must exist to the chamber beside the chamber being fired.

Let me try another beginning. The bullet was stuffed in with a little powder around it or it was loose.

One more time. The barrel begins where the cylinder ends. Hot gasses bouncing off the barrel back into the next cylinder can be a bad thing.

One more time: The flash gap can ignite the shell beside it if certain conditions exist. If that happened I would expect to see exactly what you see.

However I have never heard of it happening except in black powder revolvers. Maybe the head on that 22 bullet was loose? (The one beside the one under the hammer)

Yes, the more I think about it, it sounds like a bullet a bit loose in the shell.

Let me be the frist to coin the phrase "loose bullet flashover".
(made a little more likely with the holes so close together)

 

[tputto]

My guess is that there may have been a bullet in the forcing cone from a dud round. Next round is fired, two bullets slam together. Large volume of gas escapes through the cylinder gap, but before it can do so it enters the adjacent chambers. This gas, combined with increased recoil, slams two shells back into recoil shield hard enough to go off. The empty shells are wrinkled, which to me seems to indicate there was gas entering from the front. Had the rounds fired without this gas burst into chambers causing it, they should be round, right? And if the gas caused the shells to dent inward before they fired, it would be likely they would not straighten up when the primer and charge fired.

I wonder what happened on the last shot from the previous cylinderful? Was the last trigger pull just a click and thought to have been on an empty shell but was not? A gunsmith might be able to confirm whether there is a bulge in or near the forcing cone.

 

[Delos]

Test Time

Looking at your picture 4 of 4, the barrel is really thick -- where it would meet the cylinder when closed. It probably covers a lot of the cylinder hole beside the one lined up with the barrel.

Someone braver than me should loosen up some 22 bullets and try to duplicate what happened to you.

 

[Delos]

Maybe?

My guess is that there may have been a bullet in the forcing cone from a dud round. Next round is fired, two bullets slam together. Large volume of gas escapes through the cylinder gap, but before it can do so it enters the adjacent chambers. This gas, combined with increased recoil, slams two shells back into recoil shield hard enough to go off. The empty shells are wrinkled, which to me seems to indicate there was gas entering from the front. Had the rounds fired without this gas burst into chambers causing it, they should be round, right? And if the gas caused the shells to dent inward before they fired, it would be likely they would not straighten up when the primer and charge fired. I wonder what happened on the last shot from the previous cylinderful? Was the last trigger pull just a click and thought to have been on an empty shell but was not? A gunsmith might be able to confirm whether there is a bulge in or near the forcing cone.

I like your theory because it accounts for the "next round" having both expansion splits and indentations near the end.

However I am clinging to mine because the shell under the hammer was bent inward on the rim corner beside the "next" shell. My theory accounts for gasses going that way slightly after the first shot fired.

 

[il Padrino]

Any possibility there was crud (unburnt powder) under the extractor star, in which case the extractor may not have been sitting flush and the recoil of the fired round causing the extractor star to actually hit the rims of the two adjacent rounds therby setting them off?
Basically the extractor itself acting like multiple firing pins.

 

[medxam]

I have seen several cases of "sympathetic discharge" from .22 rim fire revolvers. I agree with RED9 that all have been in cheap lose "Saturday Night Specials". The theory was that the cylinder was so lose that the rounds struck the rear of the gun during recoil and discharged. In the ones that I have seen, the projectiles exited from the cylinder. They could easily be identified because of a scalloped nose from striking the frame as they went on their way. I had one case in which a female was dead from two bullet wounds to her chest. Her boyfriend was in the room at the time that she was shot. He claimed that they had had an argument and that she took the gun and shot herself. The LEOs were sure that it was a homicide and that he had shot her because she had two fatal GSW's. When the projectiles were recovered, one had the scalloped nose, confirming "sympathetic discharge" and possibly confirming his story, OR, he shot her and was very surprised that two rounds discharged. He was acquitted, but shot to death by his ex-wife a month later.

medxam

 

[Delos]

I'm right, everyone else wrong (maybe)

Any possibility there was crud (unburnt powder) under the extractor star, in which case the extractor may not have been sitting flush and the recoil of the fired round causing the extractor star to actually hit the rims of the two adjacent rounds therby setting them off?
Basically the extractor itself acting like multiple firing pins.

Nope, that does not account for the rim being smoothly bent toward barrel. Everything would be crushed backward if you guys were right.

Maybe the back end of the barrel needs to be tapered like the old black powder revolvers. Maybe they have reached the limit of how many rounds can be in a 22 cylinder. 10 might be too many without tapering the back of the barrel.

 

[Jaymo]

That's the first chain fire I've ever seen, with a cartridge gun.

 

[ImprovedModel56Fan]

I'd say a case head rupture set off the next round. Reason for the recessed case head cylinder. But I just drive the truck.

I am no expert, and I'm just throwing in one more opinion based on a little knowledge and a recollection of history. I think that charlix nailed it. Historically, the reason for recessed case heads was a fear of exactly this, and if you look at the rear of the 617 10-shot cylinder, you see that that design protects the shooter, more or less, but does nothing to prevent adjacent detonation. Maybe someone more knowledgeable than I will explain how that's not true, but that's what it looks like so far. Guess my old 6-shot K22 isn't as outdated as I thought.

 

[scooter123]

Charlix has identified the cause. Rimfire ammunitions have a long history of casehead separations, it's why the cylinders on the 22 caliber revolvers are still recessed today.

Unfortunately with the 10 shot cylinder there isn't a complete circle enclosing the caseheads, so there is a "burn path" for the gas jet to adjacent chambers. Since these gas jets are quite hot it causes the adjacent round to cook off. It's one aspect of the 10 shooters that I find a bit problematic. Good news is that rimfire ammunition today suffers casehead separation at a rate that is probably 1/100 to 1/1000 that of 100 years ago. That is a result of significant improvements in metallurgy. Basically, I think this is likely a 1 in 10 year event and it may be 1 in 100 years.

 

[Delos]

An easy test?

In his picture 4 of 4, look past the cylinder at the rear of the barrel. There is twice as much steel there (around the hole) as on my wife's model 66-3 357 mag.

That barrel is probably fine for a six shooter but much to thick for a 10 shooter (in my opinion). Without seeing one up close I guess the barrel covers at least one third of the end of chamber of neighboring round.

When the blast comes back off of that into the neighboring chambers it is no doubt hot. Need to put an empty fired shell with a little gun powder in it, in one chamber. Put a 22 long rifle next to it, and fire it, to see if it ignites the powder. If it does-not then that ends any of my speculation about flashover.

(But with the powder from a 22 rimfire burning for about 16 to 18 inches of rifle barrel - I think I am right).