What PSI for a .38 Special K-38 Would Blow Out the Cylinder and the Top Strap?

[Crecy]

I have a K-38 that has been destroyed by an overload (not by me). There is no bulge in the barrel so I suspect a double charge of a correct powder or a charge of a wrong powder. The chamber that the round was in and the two adjacent chambers are destroyed and the top strap is peeled upwards like a banana. I see from the 'net that .38 Special PSI is around 17,000 for regular loads and 20,000 for +P loads in modern handguns. As a guesstimate what level PSI would be required to do this sort of damage?

I have searched the net and cannot find what is the PSI that they use for proof loads for .38 Special. I have checked the SAAMI website and they don't specifically list the data. I would like to know what that PSI is since it would seem to be the level that won't destroy the revolver and then I could have a point to guesstimate what the PSI was for this event.

(This is similar to what can happen with a Webley that has been 'shaved' to accept .45 ACP rounds. There is a sticky thread about this in this forum which links to pictures on the British Militaria website. I have seen figures that the operating pressure for the .455 Webleys to be in the 12700 to 13200 psi range the latter specifically cited for the Mark VI, which along with the Mark V, was the only one designed for smokeless powder. The .45 ACP is stated to have a standard operating pressure of between 19000 to 21000 psi depending on the source I read. There are pictures on the 'net of .455 Webley cylinders which failed with .45 ACP rounds. So it seems that something in the range of six to seven thousand PSI beyond the standard operating pressure is enough to blow the cylinder. I have also read, can't find the source now, that the .45 ACP round pressure is higher than the proof load pressure for the Webleys. I acknowledge that the metallurgy in the early 1900s was not as good as it is now and that may contribute, to some degree, to the Webleys fracturing with the .45 ACP round.)

[Outpost75]

A double charge in .38 Special will not blow the cylinder. It takes a combination of multiple charges and increased seating depth which compresses the powder above 100% of load density.

[Crecy]

A double charge in .38 Special will not blow the cylinder. It takes a combination of multiple charges and increased seating depth which compresses the powder above 100% of load density.

Ah ha! Thank you. It is a very informative chart, interesting how incorrect air space/seating depth can turn a 'regular' load into a bomb. I find it not only interesting but remarkable, the last load on the right is running over 70000 PSI! So one can hypothesize that what happened is that a regular charge of powder with an incorrectly seated bullet, was more than enough to blow the cylinder and the top strap.

[Hick]

Any numbers on stress in the cylinder wall are iffy-- because its hard to really know exactly how something like that will fail. However, it happens that I had, at one time done stress calculations for 38 Special +p (20,000 psi) in my S&W Model 64 38 Special. My calculations using standard engineering equations came up with an estimate of 44,750 psi tensile stress in the cylinder wall at the thin outside web, and 59,200 for shear stress in trying to blow out the side of the cylinder. Yield strength depends on the steel used but is often something near 100,000 psi. So--assuming my calculations are reasonable, it would take a cartridge pressure of something over 35,000 psi instead of the 20,000 for 38 Special +p. That's one heck of an overload! My hand calculations are a simplification-- the cylinder is a complex shape-- so don't take this for absolute truth, But I think its close.

[Outpost75]

Determining factor in cylinder blow and top strap failure is whether you get symphahetic discharges of rounds in the adjacent chambers. If this happens all bets are off.

[alfadan]

Sure sounds like a squib barrel obstruction followed by a double charge.

[wilecoyote]

It happened to me the first time I reloaded_
36 Chief, 2"_
I still wonder today if a double charge under a hollow base wad cutter could have created a squib, melting the center of the wad cutter, lodging it in the barrel without letting it come out, until the next shot, etc._ after 24 years, I ask this question to the top names who have already answered here_
thanks to all_

[Crecy]

Dear alfadan,

I can't conclusively prove that it wasn't, I got the revolver second hand and wasn't there when the event occurred. The only thing I can tell you is that the barrel is smooth and I can find no evidence of any bulging which I would expect with a squib load then another bullet. Having said that I find wilecoyote's hypothesis to be very interesting since you can think of a situation with a) melted center squib wad cutter b) next round pushes out the wadcutter but because it is partially melted and more easily displaced than a regular bullet stuck in the bore it doesn't have the same resistance and create enough of an obstruction to cause a bulge. I freely admit that I am having trouble squaring the logic of melted wadcutter that is enough to cause cylinder and top strap rupture without leaving a bulge, but it is "never always and never never."

[wilecoyote]

Dear alfadan,

I can't conclusively prove that it wasn't, I got the revolver second hand and wasn't there when the event occurred. The only thing I can tell you is that the barrel is smooth and I can find no evidence of any bulging which I would expect with a squib load then another bullet. Having said that I find wilecoyote's hypothesis to be very interesting since you can think of a situation with a) melted center squib wad cutter b) next round pushes out the wadcutter but because it is partially melted and more easily displaced than a regular bullet stuck in the bore it doesn't have the same resistance and create enough of an obstruction to cause a bulge. I freely admit that I am having trouble squaring the logic of melted wadcutter that is enough to cause cylinder and top strap rupture without leaving a bulge, but it is "never always and never never."

thank you for taking into consideration my hypothesis, formulated by me, admittedly ignorant today as just under 24 years ago_ I can only add that a 2" barrel like mine would hardly have shown bulging, precisely because of its shortness, before the melted center, hollow wadcutter, could be expelled by the next shot. but still I remain in the field of my hypotheses, and ready to listen all_

[racepres]

^^ While I have a Very hard time wrapping my mind around anything Melting... I know that an overloaded Hollow Base Wadcutter, especially Soft Swaged, can/will shed its "skirt". The Skirt, tho hollow, is Now an Obstruction. The Next round will jam up behind it..There are untold examples of sectioned Barrels with stacked up projectiles in them...and Eventually the Shooter will become aware that there is a Problem.. To Blow the Top off a Revolver. There must have been considerably more than a Simple Overcharge. I cannot imagine how much energy is Required to explode a Cylinder, let alone blow off the topstrap.. And I have witnessed NitroMethane "blowups".. now there is some Energy!

[wilecoyote]

^^ While I have a Very hard time wrapping my mind around anything Melting... I know that an overloaded Hollow Base Wadcutter, especially Soft Swaged, can/will shed its "skirt". The Skirt, tho hollow, is Now an Obstruction. The Next round will jam up behind it..There are untold examples of sectioned Barrels with stacked up projectiles in them...and Eventually the Shooter will become aware that there is a Problem.. To Blow the Top off a Revolver. There must have been considerably more than a Simple Overcharge. I cannot imagine how much energy is Required to explode a Cylinder, let alone blow off the topstrap.. And I have witnessed NitroMethane "blowups".. now there is some Energy!

...thanks, racepres: your observation also makes sense about what I find difficult to express in suitable terms, this without prejudice to the fact that in my blow-up one or more wrong loads played their part_and this combined with the concept of sympathetic explosion already mentioned, (and which I would not have even considered) , of course_

[Electrod47]

I ran into a "slight acquaintance" in the desert around 1979. He was target shooting and I joined him. I noticed he had a large red scar across his right cheek. He opened his mouth and pulled back the cheek to reveal all the teeth on the top part of his jaw were gone and looked like his gums had been sewn up. He said his Smith and Wesson 2" Detective blew up and the top strap had been lodged in his jaw and a ER doctor had to dig it out......Said he was gonna sue S&W...I never knew how this story ended, But, I remembered once earlier overhearing him tell somebody at the local gun club that he had a formula for duplex loading a handgun..............................

[racepres]

^^^ Takes All Kinds...
I would not been able to help but ask that individual if he was Suing because S&W made some Bad Ammo!!!!!!

[rintinglen]

Actually, a double charge can blow up a gun. The study done by Hercules was specific to the mid-range, 2.7 grain 148 wadcutter load, which was very low pressure, yet a double charge boosted pressures nearly 4 times into 357 magnum range. Had that been a max load with a 158 grain boolit, 4.2 grains at 16,000 CUP, a double charge of 8.4 grains of Bullseye would almost certainly yield pressures well over 50,000 CUP, perhaps over 60,000. Not an experiment I care to conduct.

[racepres]

Actually, a double charge can blow up a gun. The study done by Hercules was specific to the mid-range, 2.7 grain 148 wadcutter load, which was very low pressure, yet a double charge boosted pressures nearly 4 times into 357 magnum range. Had that been a max load with a 158 grain boolit, 4.2 grains at 16,000 CUP, a double charge of 8.4 grains of Bullseye would almost certainly yield pressures well over 50,000 CUP, perhaps over 60,000. Not an experiment I care to conduct.

My Curiosity demands that I ascertain just how Much pressure is required to do such Damage.. My wonderment is that it May be Cumulative Damage ...but..Maybe Not. That and would the Barrel as well as BC gap need to be Plugged to Contain it All??
The Sympathetic ignition of other cylinder charges seems suspect as well...how was the Pressure contained??
I did have a Chain fire in a Black Powder Sixgun once... very disconcerting...but..not a High Pressure thing at all...

[376Steyr]

I would lean towards the cause was accidentally substituting the wrong powder. There are plenty of old loading sources out there which call for very healthy doses of H2400 powder in the .38 Special. The same weight of Bullseye would be a triple charge.
Years ago, one of the Boise gunshops had a Ruger Super Blackhawk .44 Magnum with a blown cylinder and topstrap in their display case, with a sign that said, "This is what happens when you get W231 confused with W296."
As for pressure, ballpark yield strength of steel is 100,000 psi in a testing machine. I'd guess it would take around 75,000 psi in a chamber to break the cylinder walls, and after that you're just accelerating the fragments faster.

[racepres]

I would lean towards the cause was accidentally substituting the wrong powder. There are plenty of old loading sources out there which call for very healthy doses of H2400 powder in the .38 Special. The same weight of Bullseye would be a triple charge.
Years ago, one of the Boise gunshops had a Ruger Super Blackhawk .44 Magnum with a blown cylinder and topstrap in their display case, with a sign that said, "This is what happens when you get W231 confused with W296."
As for pressure, ballpark yield strength of steel is 100,000 psi in a testing machine. I'd guess it would take around 75,000 psi in a chamber to break the cylinder walls, and after that you're just accelerating the fragments faster.

This got me thinking more (dangerous I know), But, The Nature of Nitro In General, results in rising pressure as long as it is Contained...but, once containment released, pressure drops Exponentially.. with Nitro Methane, nearly Instantly. I cannot fathom any acceleration being achievced, with No Containment.

[rintinglen]

The pressure is contained, right up until the cylinder wall releases. Just as a bullet is accelerated to a higher velocity by increased pressure, so too the metal fragments when the casing of a bomb lets go--which is what our overcharged cylinder has become. The military has extensively done studies on bombs and explosives considering these matters.

[376Steyr]

This got me thinking more (dangerous I know), But, The Nature of Nitro In General, results in rising pressure as long as it is Contained...but, once containment released, pressure drops Exponentially.. with Nitro Methane, nearly Instantly. I cannot fathom any acceleration being achievced, with No Containment.

Oops. I can see how I confused you. My intention of "and after that you're just accelerating the fragments faster" was that pressures above the theoretical breaking point of the cylinder would result in the velocity of the fragments increasing proportional to the increase of the pressure. You are correct in pointing out that once the force is removed, the mass will no longer accelerate.

[racepres]

The pressure is contained, right up until the cylinder wall releases. Just as a bullet is accelerated to a higher velocity by increased pressure, so too the metal fragments when the casing of a bomb lets go--which is what our overcharged cylinder has become. The military has extensively done studies on bombs and explosives considering these matters.

Accounting for an explosion...if Pressure is Not contained... but... there is a Reason Liquid, under pressure, does Not really cause a big explosion...it does Not Compress...