[halfmile]

Pressure should never be a problem since proofing is roughly twice that of expected pressures.

The rest of your missive brings a question:

Where are the bright boy metallurgists, engineers, and lawyers that belong to the manufacturers if this is more than just a shot in the dark?

I understand your staements and have to agree with them.

But then I don't make or sell shotguns.

HM

 

[635 G]

Just about every manufacturer from low end to high end guns--has a disclaimer in their purchase & or instructional documents. In our litigious society it is a way of subrogating blame to the user. if you feel your gun is in danger of blowing up, use factory ammo. This way you have more than one person to sue, and the gun manufacturer and ammo manufacturer will be pointing fingers at each other & you for not maintaining the gun by sending it back to an authorized service facility for its annual.

Lou

 

[Gold E]

Proof testing is a one time pressure cycle which, at two or more times the typical shell induced operating pressure, only adds to the cyclic stress regression of the pressure vessel. Unfortunately, I don’t believe that there exists a non-destructive method of determining the linear (logarithmic) regression curve of a vessel; only accelerated methods.

 

[TOOLMAKER 251]

Dan Orlick had well over 1,000,000 rounds thru his Ljutic. I know a Pa shooter who got a K80 when they first came out and has over 300,000 thru his with no problem. Anothe guy has 500,000+ thru his TM-1 no problems.

 

[Gold E]

Mr. Kaufman,

I agree, although I believe it would require a Vickers test to determine relative yield stress; perhaps a better indicator of work hardening. Cyclic testing would ultimately provide the most reliable empirical data relating to a Cyclic Life Limit, if I may amend your phrase.

 

[Gold E]

Good point PBigBore.

 

[just_bob]

Everything under stress will fail eventually. Flaws in material, manufacture or heavy use can accelorate this. I for one would gladly pay a resonable price for periodic inspection if we can identify barrels going bad with a high level of accuracy. Otherwise, statistically it would seem that most are built with reasonable service margin.

 

[joe kuhn]

I've heard of a test where you push hydraulic fluid into both ends of a barrel until failure.

I've also heard that European mfrs rejected this test as a standard.

I find it ironic that a European discovered the planets going around the Sun when his measuring instrument was improved.

We need a new measuring instrument. The same instrument could be used for new and used barrels. I'd be real interested in the numbers. The truth will prevail, eventually.

Joe

 

[JBrooks]

"I BELIEVE IT IS THE RESPONSIBILITY OF THE MANUFACTURER TO STATE WARN AND MAKE KNOWN THE LIFE LIMIT POTENTIAL"

Where to you suggest to mount the Hobbs Meter?

 

[joe kuhn]

Don,

If the gun makers wanted to suggest a replacement interval, do they even have the data they need to make such a suggestion?

 

[Gross Man]

Aircraft manufactures do accelerated life testing, where they cycle the components through thermal, shock and vibration testing. This is usually done to failure. From this data they establish an inspection schedule and component life. Logs are kept, and hopefully no part fails in operational usage. I doubt gun manufactures do anything similar. Lets check with our favorite gun service people and see if they have any factory recommended inspection procedures as part of their annual service. Bill Gross

 

[TOOLMAKER 251]

My Perazzi MX2000 owners manual states "make sure to use shotshells of the same gauge of the gun you are using" My MX8 says just about the same thing. No mention of reloads, only about internal or external altering which voids the warranty.

 

[smifshot]

Its not necessary for me to say I dont know anything about the strength of metals barrels are made from. I'd like to ask if DG Kaughman is the same shooter I knew many years ago? At that time he was a young skeet shooter, a very good one and lived in Texas. If you are one and the same, a hearty hello and good wishes from the poor state of Mississippi. Smoker

 

[Laudygirl]

Would the firearms maker then have to make public (or stamp) the original thickness of their barrel as when new?

When you have brakes replaced a good shop will "mic" the rotor or drum for wear. If it does not meet minumin standards they recommend replacement before new shoes or pads are installed. And I belive that minumin is on the drum/rotor?

 

[Dednlost]

Proofing will show if there is any defects in the gun at that time, in other words if you had a void in the metal it would give away when exposed to the proof round which is much higher pressure than a standard load. So that pretty much tells you that a proofed gun isn't leaving the factory with a defect in the metal.

You could take any barrel and shoot enough proof loads thru it until it failed, but that doesn't mean the gun is defective. I suspect some shooters expose their guns to loads in the proof range either by accident or on purpose when they try to maximize them for the games. So any gun will take only so many overpressure loads before it is destroyed. The higher the pressure the less of them it will take but I don't think that means that many thousands or millions of standard loads will do the same thing. I don't care how many times you hit a big anvil with a 1oz hammer it will never hurt the anvil.

Nondestructive testing done by a good lab will tell you how much pressure the gun was exposed to. This will tell a lot, I'll bet the K80 was exposed to many times the pressure it was built for. The question is what caused the pressure?

No matter how long you've been reloading you can make a mistake, anyone who says they never make mistakes or it can't happen are either very lucky or just haven't had their turn yet. Just like AD's it's not if but when.

I'm also very suspicious of cases that have been used too many times. I see guys with raggedy cases on the line all the time. I don't know the answer to this as far as shotgun cases go but what is the job of the case beyond the obvious? In brass case reloading the case expands and takes up some of the pressure as its transferred to the chamber wall. What if the plastic case has been used so much it's lost its elasticity? What if it let go in one spot allowing all the pressure to be applied to one small area of the chamber wall? The rate the plastic case opens up under pressure is surely much different on a overused case than on a new one, a possible problem to look into.

Most of the time with these kinds of incidents we find there is no one thing to blame, it's usually a set of circumstances that come together in an unfortunate way.

 

[joe kuhn]

Nice discussion.

With the hydraulic pressure test, fatigue could be measured as the difference between the burst pressure of a new barrel versus the burst pressure of a used barrel. Say a barrel bursts at 50,000 psi when it is new and 20,000 psi after 1 million rounds. Standards could be set. Burst pressures could be measured at zero, 1/2 million, 1 million and 1.5 million rounds to see if the burst points form a line or a curve.

I can easily imagine that a pressure test device could be used to put 1 million rounds through a barrel by applying 10,000 psi over and over again. That however, may not be the same as a round moving from one end of the barrel to the other. I'm sure we could contrive a test to check the two events.

I've heard a slow motion video of a shot fired through a barrel looks like a snake swallowing an egg. This is different from an even 10,000 psi hydraulic surge with hoses on both ends of the barrel.

I believe a hydraulic test device would even shed light on possible user error. When the burst curve is known for a barrel, with approximate use and the pressure of certain loads, we would know alot more than we know now.

Your thoughts?

Thanks Don, Joe

 

[joe kuhn]

The non-destructive tests are? (Maybe I missed them in my reading of the above)

Yes, we need mfr life limits.

 

[TOOLMAKER 251]

You would have to build a test fixture to apply lets say a hydraulic pressure of 10,000 PSI with a shift valve to go back to residule pressure cycling every 10 seconds or so and not allowing the steel to go over lets say 150 degrees. The piece tested would have to be of the same type of steel and dimension as the shotgun barrel to be tested. You would only need a barrel maybe 6 inch long with chamber and forcing cone. Then let it run for several days or maybe 250,000 cycles. This would only test the type of steel and not any given lot #.

 

[joe kuhn]

Cool.

My notes from Don's writings - "The Non-Destructive Tests are Magnaflux, X-Ray, Zyglow and Rockwell in addition ther are several hight dollar "Space Age" computer driven Laser and Harmonic tests."

Will spin off another thread about barrel life limits for military guns.

 

[Bruce Em]

Excellent thread, exactly what I was hoping for when I posted on the longer "true story on the K80..."

Also Oops Kaboom" that shows separated shells pulled apart by crimp opening force.

Cyclic fatigue limits are assumed values for a given proof load but are more closely related to meatlurgical properties like hardness etc.

Barrel dimensions are only relative and would require interpretation of the changes over the life, not just a present day diameter vs length reading.

NDT is simple; either ultrasonic or eddy current could identify flaws from the inside of the barrel. The relationship with initial flaw size and cyclic fatigue is well known. I wonder if anyone in the shotgun industry uses it?

Cyclic stress is higher and the number of cycles is higher in shotguns than any other firearm even though the pressures are relatively lower.

These are thin wall pressure vessels and they see only cyclic stress. Stresses are higher in target shells than in magnums as the pressure pulse is much sharper even though it is short.


I do believe multiple factors are to blame such as number of shots, bbl fouling with plastic, stress risers, and user error (separated tube from base.


as I said before, I do not know and but for the grace of god, go I.


I bet one could develop a bbl mounted RFID or remote reading cyclic strain gauge hidden under the forearm

An overall database of burst info would be interesting to see. Is it the high volume reloaders that get it or the low volume user accident? fast powder vs slow, cleaning cycles etc; there are a lot of factors.

your thoughts?