Well, yes and no.
There is the fatigue limit. Any loads below the fatigue limit can be withstood infinitely, loads over the fatigue limit will fail the part through high-cycle fatigue (millions of cycles).
In the case of the M16/AR bolt, the loads are not only above the fatigue limit, in some areas they are above the yield limit. Repeated loading above the yield limit will result in low-cycle fatigue (hundreds to thousands of cycles, depending on the loading)
Below is a stress diagram of an M16 bolt loaded to about 58,000 psi. You see that tiny area of red in the fillet of the lug? There the stress in the steel has exceeded the yield stress and this is where low-cycle fatigue cracks will form. Faster if you have a corrosion pit or something like that. The M16 bolts was designed to withstand repeated loading of 50,000 psi, over the years, the working chamber pressure as been bumped up, and life has been reduced.
Does one shot with 70,000 +/- 10% psi (125%) reduce the fatigue life? Well, the little red spots on the stress picture would be slightly bigger, so yes. BUT, by how much? It will be more than one, because the stress is at least 125% higher. Low-cycle fatigue has an estimate range in the order of 50%, meaning, if a model shows you will get 10,000 cycles before failure, in a population of parts, you could get some fail as low as 5,000 or last until 15,000 cycles.
It just might be me, but I am confident that the life reduction of ONE 125% over-pressure event will be lost in the broad uncertainty band of fatigue.
Last edited by lysander; 08-01-19 at 18:56.
Possible example I think most have heard of.
No first hand experience (reading only), but I would think the steady use of 5.56 proof loads would be similar to .38 Special +p/+p+ through older S&W Airweights. The claim was never a Kaboom from 1 round or even occasional use, but (so the story goes) everything would get worn and loose at a much faster rate than if standard pressure loads were used. Heard a similar story about a cop who had fairly unlimited access to department +p+ 9mm, picked up a Browning Hi Power, and proceeded to trash it fairly quick.
Last edited by jsbhike; 08-01-19 at 19:44.
Patriotism means to stand by the country. It does not mean to stand by the President... - Theodore Roosevelt, Lincoln and Free Speech, Metropolitan Magazine, Volume 47, Number 6, May 1918.
Every Communist must grasp the truth. Political power grows out of the barrel of a gun. Our principle is that the Party commands the gun, and the gun must never be allowed to command the Party Mao Zedong, 6 November, 1938 - speech to the Communist Patry of China's sixth Central Committee
I believe 100٪ proof testing is a relic of a time when metallurgy couldn't always be assured, and when cracks and inclusions in material were more common.
Nice diagram lysander, likely explains why LMT radius at the bolt lug/body interface.
This and the HendersonDefense post are legit the only parts of this thread that aren't just prattle.
If you aren't an engineer, you don't know what "proper" means. You can read the spec, but that's about it.
There's exactly two ways to view this problem: empirically through experience (Henderson Defense) and scientifically through training and study. Any other is snake oil salesmanship.
Canadian C7 bolts use 9310 and have life cycles that make the US MilSpec bolts look like child's playthings. C158 isn't a magical material found only in meteors fallen to earth. It's a steel. There's a ton of flavors of steel, and there are people whose life's work is to learn about, study, and apply their experience and knowledge towards practical ends. We call them engineers.
Meanwhile, 7 pages of navel gazing and "proper [this]" or "proper [that]" and we've had only a handful of meaningful posts.
Nitriding was not a mainstream surface treatment at the time that the AR15/M16 family of weapons was designed. 5-axis CNC machining didn't exist then, either. Neither did cell phones. Mu****as went to the moon with aluminum slide rulers. Things have advanced a bit since then, considering that your back pocket holds more computing power than even what went up in the first space shuttles.
Buy a bolt and shoot the shit out of it. Toolcraft is an OEM, so if you're worrying about "proper [this]" or "proper [that]", pay a company that supplies other vendors.
- Jeff
“Every record has been destroyed or falsified, every book rewritten, every picture has been repainted, every statue and street building has been renamed, every date has been altered. And the process is continuing day by day and minute by minute. History has stopped. Nothing exists except an endless present in which the Party is always right.” ― George Orwell, 1984
Fun-Fact-for-today: Carpenter developed 158 as a die mold steel, and that still is its primary use.
Another Fun-Fact: AISI 9310 is a very popular steel for machine gun bolts. The M60, M240, M249, and I believe the bolt head for the M134, all use AISI 9310. And, 9310 was approve as an alternate material for M14 bolts.
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