12L14 steel strength

[razorbritches]

I haven't heard of anyone ever testing sight dovetails to destruction. I suppose you would have to file progressively deeper dovetails, install a rear sight that fit each one, and fire a proof load. Then rinse and repeat till a failure occurred this would give a realistic idea of what that magic number is. It would also require several failures to prove that magic number. Was it me I would go with the numbers already provided in this discussion, but should anyone have info on such destructive testing I would be very interested.

 

[Scota4570]

Sam Fadala did some testing, along these lines, in the 1970's. He made "barrels" out of electrical conduit. Those barrels withstood respectable charges of BP and patched balls. The first time a ball was short started they bulged or blew out.

My personal opinon is that properly loaded MLs don't bow up due poor materials. They nearly always blow up due to loading wrong. It could be short started, smokeless powder, multiple loads, who knows? People get creative when they destroy guns.................IMHO.

 

[jerrywh]

In regard to thin portions of barrels a dove tail that is thin does not equate to the same thing as a barrel that is thin all the way around it's diameter as far as the strength of the barrel goes. Ask Zonie. The reason is, there is a lot of surrounding metal to support the section where the dove tail is. Pressure down at the muzzle in the location of the front sight on a rifle or even a pistol is very reduced. A dovetail in that area can be almost paper thin and will probably still be safe. I have tested barrels that were only .030 thick at 10" from the muzzle with a charge of 150 grs of ffg with no negative results. The metal was 1137 annealed.
In regard to another statement made a barrel that was well made and had a wall thickness of at least .200 and made of seamless tubing blew up in pieces when properly loaded with only 80 grains of ffg and one round lead ball of .750 diameter.
I do not know why it blew up but the man who tested it was very experienced and was a machinist by profession. His name was Jim Wolford and he wrote an article on blunderbusses for muzzle Blast Mag. I still have the article. There are flawed barrels out there but they are very rare and almost always come from individual makers and not from professional barrel makers.

 

[Col. Batguano]

Do we have any numbers that we can use for calculative purposes; elongation, tensile strength, ductile strength etc? For instance a 12L14 hot rolled number of 22 is a nice number to have, but what does it mean when it comes to strength?

In the context of this discussion, the thinnest point of the dovetail will be the weakest point. But, because of the high elongation factor the thin area can "borrow" some strength from the surrounding metal on either side of the thin area. At the muzzle it can't, which is why cannons have a muzzle swell--to give them more material for strength. With a larger caliber (62 vs. 32 for instance) the arc of the bore is more gentle, and the thin area is thinner longer, which means that you will need more metal between the dovetail and the bore to achieve the same safety factor.

Destructive testing certainly COULD be useful, but I think because of the homogeneous nature of today's steel that we could probably be close enough if we went with the formulas and calculations.

For instance as a purely speculative hypothetical (meaning I have no numbers to back up what I am saying); after being subjected to the shock load firing of 1000 rounds, and a pressure of 8000 PSI for .008 milliseconds, with a curve of 3F's burn rate, the elongation factor of hot rolled 12L14 with an unsupported thickness of .10 will be reduced to 18, and the brittleness has increased to 12. After another 20,000 rounds the elongation would be reduced to 6, which reduces your safety factor to .2, and after which a catastrophic failure could be expected within the next 1000 rounds.

We could then calculate / infer the failure points of other thicknesses, without having to go to all the trouble of many many thousands of rounds to get to the catastrophic failure point.

As an analogy, in commercial aircraft, the number of "cycles" on the pressurization of the cabin is kept track of, and, after a certain number of them (say 20,000 or so) the brittleness of the aluminum will have increased to the point where failure can happen. Remember that Aloha Airlines 737 that turned in to a convertible about 30 years ago? That's an example of metal fatigue, or increased brittleness that was unfortunately, tragic.

Somebody like MD or Zonie please chime in here.

 

[Zonie]

I'm not sure where you got the information to determine the reduction of a materials elongation?

There is no easy way to calculate this value to my knowledge.

As for fatigue calculations there are so many variables that come into the final result that coming up with a usable answer is almost impossible.

Also, aluminum is very sensitive to fatigue so while using it as an example does make your point it is somewhat misleading.

Even the poorest steels have vastly larger fatigue properties when compared with aluminum and most other materials.

Failures in steel parts are usually classified as "high cycle fatigue" failure.

How high does one need to go to consider it as a "high cycle fatigue failure"?
We're talking about millions of pressure cycles, not 10 or 20 thousand.