Overcharges?

An Overcharge doesn't make a rifle unsafe to fire, does it?
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What do you think a proof load is????

As others have stated, "safe" or not depends on specifically what the overcharge was and the individual rifle it happened in.

I know of a Remington rifle (.308Win) that got fired with about a half case full of pistol powder. Case rupture, vented gas, some small parts broken, too a gunsmith to open the action and remove the ruptured brass.

Indications were it survived 90-110,000 psi. Rifle was repaired and returned to use, and has been fine for over 40 years since.

A different rifle model might not have fared so well.

Remember that the listed MAX loads are NOT max loads for blow up safety, they are the safe max WORKING loads with the particular combination of gun and ammo components tested.
 
What do you think a proof load is????
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American's seem to think a proof load is a destructive load, I think they got that from Hatcher's Notebook. A proof load is, more or less, a historical test. Most of the proof loads are a 30% over standard load. It is not meant to blow up the rifle, but rather, to put a calibrated one time over stress situation. You could call it a workmanship test, and prior to 1920, it would have been a valid test. I am of the opinion that in today's manufacturing environment, with consistent materials, and consistent production processes, that a proof load is un necessary.

Very high pressures will blow up a gun, but so will metal fatigue. Don't discount metal fatigue. The British Comet, an early jet airliner, three of these jets fatigue fractured with a loss of everyone on board.
 
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Doesn't the term "overcharge" pretty much say it all?
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Yes, again, I was accused of being involved in some very risk stuff. I did not agree.

Then I purchased 4 rifles for $25.00 each with the understanding they were suspect, I did not agree, I tested all 4 receivers with one barrel and one bolt. The length of the chamber varied .001" from one receiver to the next. With the loads that were considered to be 'risky' the length of the chambers did not change.

There are loose barrels, tight barrels, then there are chambers, I am the fan of cutting down on all that case travel. I want nothing between my case and the chamber but air, not a lot of air, I understand air is fluid, I understand air flows, I understand air can be compressed.

F. Guffey
 
Mosin, a lot depends on what cartridge and what type powder is being used. 5 grain overcharge in a .30-30 winchester and a 5 grain overcharge in a .30-378 WBY are a world of difference in what they will do to the pressure. .30-30 is a small case that uses fast powder. 5 gr over would be devesdating. .30-378 WBY. Huge case, extremely slow powder. 5 gr. overcharge would probably not even blow the primer.
 
I think an overcharge of more than a few percent could yield the bolt or cause micro cracking that would propagate. I would bet that those cracked bolts have seen many hot loads.

I would expect a single hot load that failed the rifle might be undetectable.

Rifles should be designed to have roughly a factor of safety of 4 which means they should not fail at MAX pressure or 4 times that when built as designed. Trouble is manufacturing can loosen up tolerances, have under spec metals, worn cutters causing a stress concentration, inexact fits, etc. so a manufactured rifle likely is still a factor of safety of 2-3. Then after shooting 10k - 25k rounds, it probably has some very minor cracking.
 
Rifles should be designed to have roughly a factor of safety of 4 which means they should not fail at MAX pressure or 4 times that when built as designed.
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That is a fine sounding standard, but I do not think it is achievable in reality today. 4X for a round that runs at 50K psi is 200,000psi, and NOTHING in a conventional design firearm (that I know of) can survive that.

Where do you get your figure of 4x, anyway?
 
If the steel is 4X thicker the chamber will not be exactly 4X stronger.
500 years ago someone figured that out.
The thin wall hoop stress formula is usually good enough, but sometimes we use Lame's thick wall formula.
https://en.wikipedia.org/wiki/Cylinder_stress

That is for blowing out the sides of the chamber calculation.
For behind the case, bolt lugs and abutments are in shear and handi rifle breech faces are evaluated with section modulus. Action pins are in double shear.

I have tried to blow up a lot of guns and predict what will fail and at what point in a work up.
120 ksi yield steel does not seem to yield with a 1 millisecond pulse of peak pressure.
The steel could be underrated or there could be a difference between static and dynamic stress.
 
Rifles should be designed to have roughly a factor of safety of 4 which means they should not fail at MAX pressure or 4 times that when built as designed.
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I am of the opinion that your safety factor is too high by a factor of two.

Safety factors are there because of uncertainty. Metals for example, don't break exactly at book values. There is a considerable variation in material strength, the book values are sort of an average. Manufacturer's data has been known to be optimistic. Then there are the uncertainties in heat treatment, mechanical fit, probably more. A new gun will have less stress cycles so you would expect a new gun to be less likely to structurally fail, all things considered. Safety factors seem to be customary more than anything else: best practices. It is my recollection that certain pressurized systems required a safety factor of eight. What safety factors are used depend on the application.

The designer hopes that the mechanical part with a safety factor of two will complete a normal lifetime with a load of one. No one should think that safety factors make things twice as strong, four times as strong, for that is not the purpose of safety factors. The item when new may be twice as strong as needed, but, due to all the vagaries of materials, manufacturing, that is unlikely. And with use, stress fractures accumulate, the strength of the material lessens, so an older mechanical part is not going to be as strong.
 
Very high pressures will blow up a gun, but so will metal fatigue. Don't discount metal fatigue. The British Comet, an early jet airliner, three of these jets fatigue fractured with a loss of everyone on board.
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The British comet: I believe it had square windows, the cracks radiated from the corner of the windows. Anyhow, there must have been something wrong with square windows because for decades after the windows have been round.

F. Guffey
 
Cracks, I have bolts that have the lugs sheared off, I have bolts with the lugs cracked, I have bolts that are identical to the bolts with missing lugs and the bolts with the cracked lugs. I will not use them.

F. Guffey
 
Some Stevens break action 410 shotguns have a safety factor of more than 20.
Some CZ52 7.62x25mm pistols have a safety factor of less than one.

I have calculated, I have tested.
After I did this stuff enough, I could predict the future.
 
One of my most accurate loads out of my .243 was a fair amount over top book load with that IMR powder and bullet combination, yet it showed absolutely no signs of over pressure at all.
 
yet it showed absolutely no signs of over pressure at all.
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A very disciplined reloader said the same thing to me. I suggested he slug the barrel, I then explained how I could accomplish the same results by changing factors. Being a very disciplined reloader he did not use factors.

F. Guffey
 
My rifle had a longer-than-normal leade, which I specified when I had the barrel fit. That kept pressures low.
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As you know, loading manuals are a guide. Because the barrels we have are different, there is really no way to know just what pressures our loads are operating at without pressure gages on that barrel. Physical evidence, which is all we can do, examine cases and primers, is unreliable in estimating pressures. Phil Sharpe has a section in his reloading book where ammunition that was pressure tested to very high pressures, looked perfectly normal after firing.

I do believe a long leads drops pressures, and was intended to drop pressures. Use those loads in a tight or short throated barrel, things would get interesting.
 
"Use those loads in a tight or short throated barrel, things would get interesting."

That's why I had only 1 .243. No chance of mixing it up.

When my Dad got his .243, I got rid of mine. I was heading off to college anyway, and no longer had time to shoot groundhogs.
 
Fataigue is what complicates things. The S-N plot below shows general aluminum and steel curves. I am using this one because the Wikimedia Commons has it labeled as free to share with attribution to AndrewDressel at en.Wikipedia.

S-N_curves.PNG


In the plot, the amount of stress you apply is on the vertical axis. The number of cycles of that amount of stress you can apply and release before the material fails is on the logarithmic scale on the horizontal axis. Note that if you applied a stress of 35,000 psi the steel shown work will last about 220,000 cycles. If you multiply that by 1.35 (normal proof load factor in a rifle) it only lasts 10,000 cycles. So that's a 20:1 difference in life for just a 35% increase in applied stress. On the other hand, if the steel were being used at stress numbers below the endurance limit level, the difference would be essentially zero because life would then be infinite for both cases. So when you say a gun is designed for some certain pressure limit, you have to ask how many rounds it can withstand at that pressure before you have meaningful information.

It should be pretty obvious that rifle strength is highly variable. For manufacturing convenience many manufacturers will make each basic receiver design cover a range of chamberings by adjusting only the size of the bolt face and the barrel bore size and chamber reamer used. Obviously, when such a combination handles everything from a small cartridge like the .222 Rem up to a wide belted magnum that doesn't leave much extra metal around the chamber, the life expectancy of these combinations will not be the same.
 
Over the last 15 years I have calculated the chamber pressure for the gun steel to yield and overloaded and calculated and overload guns.
Thin wall hoop stress, thick wall hoop stress, pins in double shear, calculations section modulus slices through the breech face, calculating shear on the bolt lugs, shear on the barrel lug, calculate the tension in the receiver with the lugs in the rear, and last month: calculate the threshold of the scope bases shaking loose with and without oil affecting static friction.

I have NEVER been able to get a failure in a gun based on the calculated stress from chamber pressure. It has been suggested to me that a 1 millisecond stress just does not do much compared to the rated tensile strength for a given steel. Plastic deformation takes time. When they plot that 4140 RC28 tensile strength, they give the sample piece of steel lots of time to stretch.

But those scope base screws do strip out with the torque and lube predicted. The torque lasts longer than 1 millisecond.
 
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