doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Model 12 burst

Here we go again.

The metallurgical test results for this one barrel section will tell us a lot about the composition of this barrel, and other barrels that were made from the same heat of steel.

These results CANNOT be relied upon to accurately tell us the composition of any other Winchester Nickel Steel barrels.

Another Model 12 barrel, of identical wall thickness, using an identical load, made from a different heat of steel, may have reacted somewhat differently to an exactly identical obstruction. This is why, when hydrotesting ((Burst strength pressure testing) is done by tube mills, the test is done on each and every tube in that heat or order. There can be variability and defects causing hydrotesting failure even within the same heat. The tubes that pass testing are sold to the customer. The ones that fail are scrapped and re-melted.

Lloyd, you are correct about your understanding of elastic limit. That limit is clearly exceeded when an obstruction such as a wad, mud, or snow causes a bulge or burst. Even a low pressure load can cause such damage when contained or obstructed by something in the barrel.

A similar thing happens with bolts and screws made of steel. And this is the main reason for torque specifications. The term often used for threaded fasteners is yield strength. Over-tightening a bolt may seem like a great idea to really hold something, but you could actually weaken it and cause it to unexpectedly break if that yield strength has been exceeded during tightening. The threads have stretched. Once that limit has been exceeded, the damage is permanent.

A repaired barrel bulge will always be somewhat weaker than the surrounding un-stretched steel. That usually doesn't matter under normal circumstances, particularly if the bulge was out further where pressures are much lower. But if the condition that caused the bulge is repeated, the subsequent damage is more likely to be worse, at the previously bulged spot.

In 1919- same exact gun as the M12. Madis in his great book on The Perfect Repeater mentions "running changes" for the M12- in this case, they removed the 19 roll stamps from the die, leaving M and 12-- why? Whom can say. Shortly afterwards, all the many patent numbers and dates were removed from the breech side of the barrel, that being the same side as the ejection port on the receiver.

Sure is a lot of "Horse puckey" spread around by dealers en re: M12's-- saw an early (4 digit sn.) M1912 20 gauge, 25" barrel, reblued, re-stocked with Bishop target grade wood, black plastic BP, Simmonds rib, with Cutts comp. and a spreader tube (2&1/2" chamber-- He's asking $2500 for this "dis=aster", and I heard him state loud and clear to a potential buyer-- "And this is one of the post-1964 mfg. M12's- a scarce gun indeed.

Lloyd: as Miller said, the obstruction causes the pressure in the barrel to rise above the elastic limit, the steel begins to stretch, and if the pressure exceeds the ultimate tensile strength, it bursts = a ductal fracture. Steel can also break as a brittle fracture.

Short version of tensile testing
The tension stress which causes a sample to break is called the maximum strength or ultimate tensile strength or simply tensile strength. The ultimate tensile strength is measured at point of fracture or the reversal point of the stress-strain curve; the specimen may stretch more before fracturing.
Yield strength or elastic limit is the stress which gives a permanent deformation of 0.2%.
Percent elongation is the lengthening of the sample to fracture expressed as a percentage: (final length � initial length) / initial length) x 100. It is a measure of ductility.

A specimen is precisely machined per specifications



Then loaded in the tensile machine and fitted with an extensometer



This is (unfortunately the low resolution) stress-strain curve for the 1898 Smith Armor Steel specimen: Yield - 57,500 psi; Ultimate - 101,000 psi; % elongation - 12.3

The Preacher is somewhat confused as to the definition of elastic limit.

Material stressed to a point below or equal to the elastic limit will return to its' original dimensions after the strain is removed. As soon as stresses exceed the elastic limit, there will be a permanent deformation. This permanent deformation does not require a defined 0.2% deformation to meet the definition of exceeding elastic limit. If the permanent deformation is even one half of that, or one tenth of that, or any measurable amount whatsoever... then elastic limit has been exceeded.

The Preacher is confusing and conflating the definitions of elastic limit, and yield strength. Simply put, elastic limit is the measure of the point of maximum stress where a material returns to the original dimension after removal of that stress or strain. The instant that permanent deformation occurs, elastic limit has been exceeded.

Keith apparently declined to read the stress-strain report. Middle on right - Yield @ .2%. "Short version of tensile testing" was the topic.

No Preacher, I was commenting on your understanding of the definitions (or lack thereof). I was not commenting on what a trained metallurgist who actually undersands this stuff reported.

The metallurgist didn't provide this incorrect definition to Lloyd... you did:



Copy-and-paste of information, along with impressive pictures and graphs, is not going to hide the fact that you don't really understand this stuff called steel... even many of the basics.

Here's a thought... Why don't you pay a good Metallurgical Engineer at METL to write your posts on this subject for you. Then you can pretend to be an expert, and fool a lot more people.

Whenever we discuss barrel bursts, wall thickness, and tensile strength it is important to clarify that tensile strength is only a part of the equation for estimating bursting pressure. If the barrel is made of Winchester Nickel Steel with a 100,000 psi tensile strength, that does NOT mean that it will withstand a 10,000 psi load by a factor of 10.

Barlow's formula P=2 S t / D
P=Bursting pressure in psi.
S=Tensile strength of material in tube wall.
t=Wall thickness in inches.
D=Outside diameter in inches.

Barlow�s refers to a pipe capped at both ends with a static pressure (a pressure cylinder). Shotgun barrels are not designed to be pressure vessels as one end is open and the pressure rises and falls quickly.

Burrard used the Alger Burst Formula, and there are others
Burst pressure = Ultimate tensile strength x 3(OD � ID) / OD + 2xID

A mechanical engineer friend with interest in barrel failures explained that the Hoop Stress Formula doesn't reliably predict shotgun barrel failure either
https://www.engineersedge.com/material_science/hoop-stress.htm
Shotgun barrels are �thin wall cylinders�
hoop stress = pr/t
p= pressure; r is the inside radius; t is the wall thickness
He was working on setting up a hydraulic pressure testing apparatus for barrels, but work and marriage got in the way.

Wallace H. Coxe, in "Smokeless Shotgun Powders: Their Development, Composition and Ballistic Characteristics" published by E.I. du Pont de Nemours & Co. in 1931 cites a study in which a fluid steel barrel was cut to 9� and capped, then a series of progressively increasing pressure loads fired. The barrel cap was blown off and barrel burst at only 5,600 psi.

A study by the Royal Military College of Science, sponsored by the Birmingham Proof House and the British Association for Shooting and Conservation, showed that an obstruction by 2 fibre wads (total weight of 4 grams) was sufficient to bulge or burst a 12 gauge barrel shooting a 28 gram (slightly less than 1 ounce) load. Peak pressure occurred 22mm (.866�) past the leading edge of the obstruction.

OTOH there are many studies documenting how difficult is can be to burst a barrel, including Greener's attempts in 1886
http://books.google.com/books?id=inQCAAAAYAAJ&pg=PA92

and of course The Double Gun & Single Shot Journal �Finding Out For Myself� series by Sherman Bell with technical assistance from Tom Armbrust esp.
Vol 18, Issue 1, Spring 2007 -
Destructive testing on a Damascus barrel with thinned walls; calculated by O.D. - I.D. and not measured.
Destructive testing using various obstructions, including a 20g shell.
Destructive testing using a shell loaded with 3 1/4 Drams by volume or 56 grains of Unique (similar to �Infallible�) with 1 1/4 oz. shot. The chamber burst with the first shot. The 3 1/4 Dram Equivalent load is 24 grains of �Infallible�, and 56 grains estimated pressure was 50,000 psi.

Appreciate the confirmation Keith. I also found the fastener comparison quite apt in further clarifying the concept. Now I can comfortably state that I fully understand why torque wrenches are so-important. Steel is really...fascinating stuff. It underpins what I consider to be the basis of a truly "modern" society. Arguably, all of the "engineering" (for lack of a better term) humans use to modify the environment (for our comfort and safety) is based on a steel foundation. Mr. Fox, thank you for the Madis reference (I knew you'd come up with it).

So...pre-1919 for this little 20 M12. Short-chambered little guns but...beautiful, well-made and quick (for a pumpgun). A shame to destroy such a thing. I am a simple man when it come to these concepts. Pre-"Krupp Floss" steel in ~1890, good damascus and steel were fairly close in burst strength, both were 55K to 65k range materials. Post Krupp, everything changed. Shortly thereafter, Winchester came out with Nickel Steel at 110K and ~100k became the new "standard" of modern and "safe". The timing of all that, in parallel with advent of nitro-based smokeless propellants, changed the world of firearms forever. Everything got faster and safer (within reason), including the cheaper guns for the masses.

Even if it isn't exactly definitive, I'd be curious to hear how this little Winchester's barrel steel does in Dr. Drew's testing.

Lost in the charts, and back and forth of the posts is the fact that this barrel would likely be chugging right along on the old gun it was part of, if it had not been seriously obstructed. Those pictures, of the barrel, out there 6� or so in front of the muzzle, are the stuff of bird hunters nightmares.
Obstruction bad, kiddies.

Best,
Ted

Lloyd, my understanding is that there is a small zone or region (for lack of a better term) between the elastic limit and the yield point that is known as the Elastoplastic region. At this point, steel and other ductile materials will still exhibit some tendency to return to normal dimensions, but because atomic bonds are also being broken, there is some permanent plastic deformation.

Then beyond this point, once the yield point is reached, the plastic deformation is the dominant factor, and it will take less strain to cause permanent stretch or deformation, until the steel finally breaks or fails.

When I worked for General Motors, before the bankruptcy, when money was no object, they sent us to all kinds of in-depth training classes. The several day class covering fastener torque and correct tightening of fasteners was taught by a Metallurgical Engineer from a company that produced threaded fasteners for industry. It was very interesting, because he actually put on many graphic demonstrations where we could see the effect of correct torque, and also see that bolts which had been subjected to a point just beyond the elastic limit were permanently weakened. We broke a lot of bolts, while watching exactly the rotational force or torque that weakened and eventually broke them. He told us that at that point, the steel atomic structure begins to react more like taffy. Of course, he showed us many graphs, SEM photos, etc. showing the structural before and after changes, but the difference was that he actually understood and was qualified to explain them, without giving us erroneous information.

About a week after the class, I watched one co-worker who had also been schooled in the same class tighten a 5/8" bolt with all his might. This guy was "strong like bull" with wrists bigger than my ankles. Even without a torque wrench, I'm certain he was at or beyond specs. He then proceeded to use a big hammer to pound on the wrench to give the nut over another full turn. I tried to remind him about over-tightening, (my reaction was something like, "holy shit man... WTF are you doing?"), but he said our instructor didn't know what he was talking about. Over the years, I watched as this guy spent a lot of time with drills and E-Z- Outs trying to remove broken bolts that he had snapped during installation. His entire set of T-Handle Allen Wrenches looked like licorice twists. Sometimes training and education is simply a waste of time and money. Some folks understand things, and some never will.

Earlier in this thread, wall thickness dimensions were given as .044" at points just before and just after the burst, and also at .038" at the thinnest point of the burst. Those are fairly substantial wall thicknesses at that point of the barrel, especially compared to very many of our light double barrel bird guns. And the Winchester Nickel Steel had established a reputation for being much stronger and able to handle stiff charges of Nitro Powders. But it burst anyway... proving Ted's point about avoiding barrel obstructions at all costs.

It might be tempting to think that the barrels were honed or struck thin at the burst point, but the thinner dimension was most likely the result of rapid thinning as the barrel wall stretched in the milliseconds prior to letting loose. Once beyond the elastic limit and the yield point, the steel started behaving more like a Bazooka Joe Bubblegum bubble prior to popping. The wall got thinner and weaker as the extremely rapid deformation happened. There is an excellent chance that the obstruction started moving, but the rapid pressure build occurred way too fast to prevent disaster. The .044" or even .038" wall thickness that would have been more than adequate much closer to the chamber under normal circumstances, was no match for the sudden extreme pressure rise behind the obstruction... even with some of the best barrel steel available at the time.

BTW Lloyd, I haven't forgotten about those pics of Rockland Furnace and Freedom Falls. Will try to get them posted soon.