The "Dangerous Eaton Carcano" - A Myth Busted - Updated 2 June

Andy,

My point is that single samples are not enough to make a statistical evaluation.

Thats like saying that because someone bought a winning lottery ticket at the corner store everyone should buy their tickets there. The history of a old rifle is unknown.

You won't reuse the ones you proof tested, but how do you know that the next one you buy or the one Joe down the street has wasn't subjected to the same kind of abuse? How do you know it wasn't cycle a bajillion times and actually has finally reached its fatigue life on the action lugs? You can't and you don't.

As always everyone has to make their own choices about what is safe and what isn't. I just wouldn't stand up and put my name anywhere near anything as uncertain as saying that your experiments tell you anything about the general class of rifles you tested two samples of.
 
Thank you very much Andy.......... :)

I really enjoyed your article and personally, I appreciated your efforts. I look forward to seeing more of this kind of work published.

I also enjoyed the rebuttal and discussion which followed. I couldn't contribute anything myself, as most people here have forgotten more about this kind of subject matter then I'll ever master, but I did learn a lot from just listening.

Most importantly, I enjoyed the class and civility of all the folks who responded. It reminded me of why this forum is such an enjoyable place for me to visit every day.

Regards,
Badger
 
Andy deserves a round of applause for taking the time to conduct his experiments, and report the results. While the number of rifles involved may have been statistically insignificant, they were selected essentially at random, from available specimens. It is not often that original and current results are made available.
As BadgerDog has pointed out, the discussion was reasoned and civil. Fortunately, there are a sizable number of CGN who are interested in the sharing of information and meaningful exchange of ideas.
 
Like Badgerdog said, I can't contribute to this either, but enjoyed it to the maximum.

One question pops up, though : The differences between M96 and M38 ....if things are like Tiriaq said, that means that the 38s are weaker ??????:confused:

ANDY, please do this test with the Swedes as well.
PS: no, this is not an offer to use my actions.... :rolleyes:
 
eltorro said:
Like Badgerdog said, I can't contribute to this either, but enjoyed it to the maximum.

One question pops up, though : The differences between M96 and M38 ....if things are like Tiriaq said, that means that the 38s are weaker ??????:confused:

ANDY, please do this test with the Swedes as well.
PS: no, this is not an offer to use my actions.... :rolleyes:
Click to expand...

No, if anything it means that the M96 will be more likely to fail due to plastic deformation, while the M38 is more likely to catastrophically fail because for the same alloy, harder usually means more brittle. That being said, the complete action heat treating used on the M38 is by no means overly brittle and probably will not fail catastrophically. Same as the M96 receivers with case hardening are certainly adequate for 6.5 Swede pressures and likely wont plastically deform, excepting reloading errors, of course.

In layman's terms, it's difficult to describe the differences between case hardening and heat treating, as well as the different resulting steel grain structures and their benefits ( martensite, Bainite, pearlite and austentite).

In general, martensite is soft and ductile while austentite is very hard and brittle - "glass-like". You get any of these grains by heating to increasingly higher temperatures and then rapidly quenching, but you can get mixes by controlling the quench over time, etc.

Engineers reference Time-Temperature-Transformation (TTT) curves for a given steel alloy to design the heat treatment for a given receiver. Here's a generic TTT curve for reference:

art14-p1.gif


Many modern receivers have a pearlitic outer shell to resist wear with usually a bainitic and martensitic blended core for ductility and toughness. Very old receivers are more likely to have a purely martensitic core due to the low carbon content of the steel alloy with a case hardened outer shell, a few thou thick, imparted by carburizing the surface and then doing a rapid quench at high pearlitic temperatures or even austentitic temperatures.

Hopefully that's not too hard to follow?
 
tiriaq said:
Rising to Andy's bait..... Just to muddy the headspace water - everyone is probably aware of who Bob Greenleaf is - when Bob was still at Savage he decided he wanted to experiment with excess headpace. Used a 110, of course, and prceeded to unscrew the barrel, firing along the way until the barrel was screwed out so far it became ridiculous. Now, this was done under controlled conditions, using new factory ammunition, with no consideration of ever reloading the brass. As long as the extractor gripped the case, the cartridge would fire. Nothing untoward ever happened, no separations, no KB, nothing. The cases fireformed, of course. With a design that poorly supports the casehead, and with brittle brass, things might be different.....
Click to expand...


I'll bite - How does the extractor pop over the rim if there's no leverage at the shoulder?
 
Thanks, Claven.
My knowledge of metal deformation stops at the flow values, and that only for the metals used in constructions.

Taking all the variables out.... begining with the general state of use and abuse of the two models compared here, grain variations (inconsistenc y) in the structure, would it be safe to assume that the M 38 is stronger? or will the 96 show signs of plastic deformation prior to any catastrophic failure?
 
prosper - this was being done in a lab. The case was positioned so that the extractor held it in place so that ignition would occur. You are correct - in a push feed action, if there is nothing to stop the cartridge, it would stay in front of the extractor. Bob's experiment was not a major research project. He was just curious about the effect of grossly excess headspace. It doesn't mean that it is acceptable to ignore an excess headspace condition.
eltorro - the Swedes routinely rebarrelled M96 actions to .308 to make target rifles. Obviously M38 actions were available, but 96s were used. It is my understanding that a surface hardened soft core receiver can experience substantial setback of the locking shoulders without a catastrophic failure. This has been observed in heavily used Chinese Mauser rifles. In general, if an action is in sound condition, it is unlikely to fail structurally even if pressures are extreme. The failure occurs when the cartridge case fails, and it is the abilty of the action to deal with the gas that determines the amount of damage that is going to occur. Some action designs are vastly superior from the standpoint of dealing with a catastrophic case failure.
 
eltorro said:
Thanks, Claven.
My knowledge of metal deformation stops at the flow values, and that only for the metals used in constructions.

Taking all the variables out.... begining with the general state of use and abuse of the two models compared here, grain variations (inconsistenc y) in the structure, would it be safe to assume that the M 38 is stronger? or will the 96 show signs of plastic deformation prior to any catastrophic failure?
Click to expand...

It's likely that the M38 is a stronger action, yes. It's also likely the M96 will have a surface that resists abrasion better than the M38. An M96 should experience serious lug setback before failing catastrophically, but this is all theory. Lab testing would need to confirm these hypotheses, if it mattered that much to someone ;)
 
tiriaq said:
snip... It is my understanding that a surface hardened soft core receiver can experience substantial setback of the locking shoulders without a catastrophic failure. This has been observed in heavily used Chinese Mauser rifles. In general, if an action is in sound condition, it is unlikely to fail structurally even if pressures are extreme. The failure occurs when the cartridge case fails, and it is the abilty of the action to deal with the gas that determines the amount of damage that is going to occur. Some action designs are vastly superior from the standpoint of dealing with a catastrophic case failure.
Click to expand...

I've recently seen examples of "set-back" in surprisingly everything from pre-war mausers to post-war commercial (FN) mausers & Rem 700s.

It is quite often found in sporterized military mausers which have been converted to other calibers (especially magnum cartridges). Depending on severity sometimes it is only noticed after removing the barrel.

"set-back" is when the bolt locking lugs become impressed into the receiver locking recesses. In essence the bolt is being forced back through the receiver while closed by the pressures involved in firing each cartridge.
 
Sometimes setback is detected because a bit of extra effort is required to open the bolt - the lugs have to ride up and over the ridge that's been thrown up. The bolt is forced foreward slightly as it is rotated to the open position. Plastic deformation is preferable to a fracture.
What is remarkable is that unfortunate incidents are so rare, given the number of firearms that are in use in heaven only knows what state of repair. I suspect that cartridge case quality compensates for deficiencies in many firearms.
 
Update - 2 June

spi said:
$100 says that it is threaded in and the set-screw is just there as insurance against rotating. I say this because of the alignment notches on reciver and barrel (chamber?) sleeve.
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You would have won the $100 had I bet against you. So, the regurgitated story that the barrels were pressed into a barrel stub and that was the root of the "weak action" has a flaw. My other four have the same tiny (1/8") set screw to keep the barrel and stub aligned.

For you statisticians and students of logic, we have four examples of a barrel screwed into the stub, and you never know, I might have the only five prototypes that were built that way, so I draw no other conclusions than that my five examples were not pressed in. If design documents existed we might know more, but sadly they appear to have been lost.

L to R - barrel with tiny indent for set screw, barrel stub, set screw, receiver

Eaton_Carcano_Barrel_Assembly.jpg
 
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Andy said:
You would have won the $100 had I bet against you. So, the regurgitated story that the barrels were pressed into a barrel stub and that was the root of the "weak action" has a flaw. My other four have the same tiny (1/8") set screw to keep the barrel and stub aligned.
Click to expand...

FWIW, I saw this rifle yesterday at Gunco. It's definitely threaded into the stub, not pressed and pinned as I have so often seen them described.

Actually, it was pretty well done and likely totally adequate if the user keeps to the ammo it was designed for.

In a way, it's ALOT like how a modern Savage 110 is barelled. Seems the stub was installed first, then the rethreaded barrel was screwed in until it headspaced. The set screw dimple was likely then drilled and the screw installed to prevent the barrel from rotating out of position. The back of the barrel itself becomes the chamber and the old stub becomes like the lock ring used to set headspace on the Savage 110 rifles.

One thing I will say... man, that cartridge case was fused into that barrel HARDCORE.

Did Jason get it out in the end? I saw him try to do so for the first 10 minutes unsuccessfully before I had to split. Any luck in the end?
 
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Claven2 said:
One thing I will say... man, that cartridge case was fused into that barrel HARDCORE.

Did Jason get it out in the end? I saw him try to do so for the first 10 minutes unsuccessfully before I had to split. Any luck in the end?
Click to expand...

He got it out but it was not easy. As shown in picture three at my first post in this thread, the cartridge head was blown off and the "new" end was about 1/8" inside the chamber. After removal, it will now only go in about 3/4" with finger pressure, leaving over 1" outside the chamber.

At "normal" pressures the brass expands easily to chamber size and springs back, the (steel) chamber expanding and springing back much less. At extreme pressures, both the brass and chamber expand quite a bit, and that expansion can exceed the amount that the brass can spring back causing the cartridge to lock in place to some extent and be difficult to extract.

In this case, what's left of the cartridge is actually reverse-tapered, being at an even 0.446" for 3/4" below the shoulder, then going back down to 0.444" and then back up to about 0.450". Inside neck diameter is now 0.277" (should be about 0.266" after firing), so even the thick part of the barrel expanded over 10 thou! That explains the "difficult" extraction.
 
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Had a rat Parker Hale .30-06 with which I was experimenting. VERY hard extraction. Removed the barrel and sectionned the chamber area. The chamber was obviously bulged, with linear cracks apparent to the naked eye. This was a reverse taper situation, like the one Andy described. The muzzle had been bulged, so I assume that the rifle had been fired with a barrel obstruction. The previous owner was very lucky; Parker Hale barrels are the only only centrefire barrels I have seen which will on occasion fracture into pieces.
 
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