Please keep us posted on the scientific findings.

That seems logical as the metal expanded the radius on the out side being greater than the inside would tear first,

Every time i pick up my GHE 20 or any other shotgun i will check the bores before and after each shot! Bobby

I am not engineer and have no experience or training in the physics and engineering involved with a barrel burst. What I find counterintuitive as a layman is the amount of pressure required to burst a fluid steel barrel is around 30,000 psi per Sherman Bell's destructive tests. How is it that a shot charge and wad being pushed by a force between 11,000 and less than 30,000 psi wouldn't dislodge and send a thin plastic base wad stuck in the bore out the muzzle before it reached a level of barrel burst pressure? Serious question looking for an answer. Perhaps the answer is the pressure builds faster than the ejecta moves but I don't know that.

Inertia will do it every time when it meets a fixed object regardless if that object is “stuck” in position.





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The term for "streching" is Elongation; one of the four basic maesurements obtained in a destructive test bar. Tensile, sometimes expressed as UTS, Ultimate Tensile Strength, Yield Strength; the point at which the specimen will no longer relax to it's original length (2") RA, Elongation, as a percentage of the pre-measure 2" measured length, and lastly, Reduction of Area, the amount the specimen reduced at the point of failure. The area at the failure of the test bar has a somewhat different appearance, dependent on the alloy, but looks nothing like those 'striations', which, in my opinion, are on the surface. I also doubt there was any linear stretching, simply because the failure area reach (1st) Yield, then UTS and elongation.
A properly heat treated specimen fails in a very predictable, and repeatable manner; the numbers only varying because of the percentage of individual alloying elements.
On average, we produced between 25 to 30 individual heats (Furnaces batches of steel) per week, and it's safe to say we would break between 6 and 20 tensile specimens per heat (not to mention creep strength tests, Charpy (V notch)Impact tests, and weld bend tests)

You are quite correct. The area of the failed tube is the CxOD minus the CxID.

Bell's burst tests were on unobstructed tubes, and, I think This tube was obstructed, and in pretty close proximity to the charge. The spike was (obviously) catastrophic. The pressures rise initially, after firing, and decrease the further down the bore they are measures. Within a few inches of the forcing cone, they're going up fast, but with no bore to go down.

I remember some work done by a Proof House, that took deliberately sealed tubes of various lengths, and measured the resulting failures. I found it while in the library at Leeds University, no doubt waiting for the pubs to open on a Sunday evening. That was an exchange year from RPI, and despite learning a lot, found the pubs dramatically more interesting than the labs.

Interesting Comment Regarding Win Wads
 

I was explaining the burst barrel using Win factory loads. One guy said he purchased some older Win 20 ga wads. When loading them something did not feel right so he took the shell apart where he discovered the wad crush leaves had snapped at the hinge. He took several wads and manually crushed them and all snapped at the hinge. In the trash they went. Not sure if this is germane to this burst barrel but it could be.

I, too, trashed several bags of the older, white AA 12ga wads. The petals would break off at the base.

Remember that smokeless powder has a pressure/burning rate curve. As mentioned, Bells bursts were open tubes. If a wad is stuck a couple of inches in front of the chamber, it is at the normal max pressure point anyway. If the obstruction holds even for a short time, the burning rate can go extremely higher and reach catastrophic levels before the wad even has time to move. Dean's inertia effect. It likely did move down the barrel quickly, just not as quickly as the pressure increased. It's the fatal flaw of a progressive powder; rate of pressure increase is dependent on the pressure.

A number of years ago I got my 20 Ga. Reproduction out of the safe to go grouse hunting. I had the gun stored with plastic snap caps, the kind that have a translucent housing that you can see a coiled spring inside it. When breaking the gun open the electors shot the caps out on the floor, but I couldn't find one of them. I searched all around the floor under all the furniture till it frustrated me. Here, when the ejector popped the snap cap out, it sheared the rim clean off and the body of the cap, slide down the barrel and lodged in the choke. I purchased the snap caps from Dillon Precision and decided to contact them and let them know the potential danger of that type of cap. They thanked me and quite offering on the web site.
Ever since that day I have have always looked down the barrel for day light before chambering a round.