is it true, or just myth?

[barnbwt]

The case will expand and seal the chamber...but has an easy vent forward up into the barrel even if the threaded plug is sealed at the end. Probably even more volume (and hence lower pressure) than if the bullet moved into the barrel on a normal shot so this is a very logical explanation to what happened.

There should be soot on the outside of the case if it is blowback, a pierced primer if it vented through the primer, or soot at the muzzle if it vented through the rifling out the end. Or a black-hole singularity if the pressures collapsed the laws of space-time.

Similar to the neck-clearance providing an avenue for escape, the very, very generous rifling leades commonly seen in pistols (to accomodate a huge range of bullet shapes) are a similar crack it could squirt out through.

TCB

 

[FlyinBryan]

I don't trust my memory on this, maybe someone else can confirm. But IIRC Ruger tested their P85 by completely blocking the barrel and firing a round without blowing up the gun. That was 30+ years ago and I may be wrong. But I think they did that as a means of demonstrating how tough they were.

yep. I read the same article. it was in the late 80's early 90's. they actually drilled and tapped the barrel and installed a super hard threaded bolt. fired the gun. removed the bolt, and test fired the pistol with no damage that would render it unusable

 

[grampajack]

Okay, just so I don't have to read through the last I don't know how many pages, someone tell me if it worked or not. Was there a video?

 

[Jim K]

Barnbwt wrote: "Which raises the question; what the heck do you even do with a test-fire gun that you know has a full 30,000PSI corked up inside it (and that's after it's had a chance to cool down)?"

Well, you open it. Hatcher, who presumably had 50k psi to deal with, just knocked the bolt handle (of the 1903 rifle he was using) up until the bolt unlocked, at which point the bolt was blown open "smartly" and the case was ejected. He doesn't mention heat in that test, but I picked up the 1911 just after the testing I did and, while I was not looking for heat, I felt nothing unusual. Besides, where would the heat come from? The burning powder would produce no more heat than normal when firing a round. There was no friction because the bullet didn't move. The escaping gas would not cause any significant heat rise. (Hatcher had more pressure so the bullet sealed the barrel. I, with a lot less pressure, made no special effort to do so, so the gas simply escaped around the bullet and the case.)

Jim

 

[murf]

Jimk,

Did Hatcher say the bullet sealed the barrel, or are you saying that?

murf

 

[barnbwt]

Besides, where would the heat come from?

I refer to the large drop in pressure from the hot gas conducting heat into the barrel steel, which yes, would heat the barrel about as much as it normally does.

TCB

 

[barnbwt]

Seems vaguely relevant to this thread;


TCB

 

[Jim K]

Sorry I didn't get back here sooner. According to Hatcher, the bullet, blocked at the front, had no place to go but to expand and seal the bore, but it never had a chance to move enough to pick up enough kinetic energy to cause the barrel to heat or expand.

The photo by barnbwt shows an extreme case of a barrel bursting under pressure, probably from firing a bullet into a barrel obstruction. Such an extreme is fairly rare; from the rest of the rig, I suspect a high energy round (.378, maybe or even bigger) fired with an obstructed barrel. The obstruction was probably about half-way through the barrel. When the bullet stopped, the energy dump heated the barrel, making it soft, so the pressure could split it along the fault lines (aka the rifling). Ordinarily the barrel would have either given a flower petal effect if the pressure peak was toward the front, or the effect shown if it is to the rear. In this case, though, the reason the muzzle didn't split is probably that it was constrained by the muzzle brake.


Jim

 

[HisSoldier]

This story was related to me by my pastor, so I know it is true, as he was there. The gun was not a 1911 but a 75MM pack howitzer which failed to fire it's last round, just as the fire base was being abandoned. They assumed it was a dud round so they tried to open the breech. It would not open! They ask the helicopter pilot to sling it out assembled which he refused to do because there was a live round in the tube.
One man finally took a large timber and wailed against the handle with it until suddenly the sliding wedge block opened and the case shot out the back so hard it was buried in the dirt behind the gun.
The interesting thing about that is that it was over an hour after being "fired", it had held it's pressure the whole time without any sign that it had even fired except for the stuck breech block.
It's hard to imagine it held all that pressure so long.

 

[RX-79G]

One assumption in this thread is that the bullet starting to move is the reason peak chamber pressures are never exceeded.

But what if the momentum of 230 grain (or even 500 grain) bullet is so high relative to the energy of the pressurized gas that it doesn't move much at all by the time peak temperature and pressure are reached in the chamber?


It isn't like peak pressure does all the work. Most of the bullet's velocity change happens at much, much lower pressures as the volume behind it grows as it scoots down the bore.

Peak pressure (21,000 psi in this case) might be peak pressure for this particular reaction regardless of whether the bullet moves or not.


And I'm willing to bet someone at SAAMI has done tests with blocked bores and could say whether there is actually a difference in peak pressure. I'd bet it his hardly different. What's going to be different is the pressure curve - how fast the pressure bleeds down from peak, not the peak itself.



With a fast burning powder like pistols use, I'll bet most of the pressure decrease is just from cooling, not pressure escaping.

In the case of the stuck artillery shell, it may have had 40,000 psi in the breech at some point, but if it even had 20 psi of residual pressure, that would drive the casing out with considerable velocity.

 

[Vern Humphrey]

Peak pressure (21,000 psi in this case) might be peak pressure for this particular reaction regardless of whether the bullet moves or not.

Bingo!

Give that man a cigar!

It is possible that pressure MIGHT be a bit higher with the blocked barrel, but not that much higher.