This 'catastrophic failure' of a Norwegian Krag occurred in Great Britain at a practice match in the Spring of 2014. It was investigated by the NRA-UK. The 23 page report was posted today on the Military Surplus Collectors Forum (under Krag rifles).

The Norwegian Krag action (#32513) was of 1897 Steyr vintage. A Norwegian match barrel was installed circa 1950 and the rifle has been in routine use and well maintained. Nicks and alterations to the action receiver ring and threads led to suspicions regarding the installer's competency.

The 'home loads' (reloads) used Norma brass, 140 grain bullet, and 34.4 grains of Accurate 2520. (This load appears just above a 'starting load' and well below Max. in one Accurate Arms table, I found). The rifle came apart on the fourth shot. The 'shooter', a neighboring 'shooter', and a spectator were injured and required hospital treatment (surgery for two and OP for the third).

The NRA-UK report noted 'grossly deformed necks' on some of the 'homeloads', which indicated improper setting of equipment. They displayed one of the fired cases, which looked normal. However, IMHO, the photo of a deformed loaded case in a Wilson gauge, appears to show a possible head-space problem, caused by excessive case length or poor adjustments. (I wish the report gave more attention to the dimensions of the fired cases and case length of the deformed necks).

Some parts of the destroyed Krag-Jogensen could not be found. The NRA-UK found no clear definite cause and called it: "A single overload event". If I understand the report's conclusion correctly, they attributed the failure to an excessive load or latent defect in the re-barreled rifle.

(The excessive pressure could have been an under-load detonation, an excessive pressure over-load, or something related to the 'funny' case necks).

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Hey, that single bolt lug held and we have visual evidence that Norwegian Krags have left-hand barrel threads. I bet our shooters can come up with a better analysis of this accident than the 'Brits' did!

(Those distorted case necks must cause a problem with neck-bullet tension. Deformed case neck pics):

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Detonation is a very plausible cause here. Fast powders and low case density are a dangerous thing in rifle calibers.  Too large a diameter of projectile could also cause this.

A note about the Brits.  There's a story going around the FAA about the Bits.  They were looking for  a way to test the windshields for their high speed trains.  They asked the FAA to borrow the "Chicken Gun" that we use to test aircraft windshields.  It actually shoots chicken carcasses at the windshield. Well, the Brits, using the Chicken Gun, busted just about every windshield the had and sent a report to the FAA for review.  They couldn't understand why all their windshields were breaking.  After the FAA read the report, they sent the Brits one recommendation.  "Thaw out the chickens before you shoot them".

butlersrangers wrote on May 10^th, 2015 at 11:20pm:

Hey, that single bolt lug held . . .

Single lug? (The usual Norwegian arrangement has two, no?)

Yeh, one forward lug, a bolt guide rib (fitted to make contact with the receiver, unlike U.S. Krag bolts), and the bolt handle root.

I guess my point was: The bolt was not the weakest link.

Hi guys, just posted this on the Milsurp forum. I'll post it here as well. Just some background info from Norway. Krags rarely blow up, but when they do, this is the usual pattern.

In the 1970's the norwegian Krag ammo was downloaded to a preassure of 2800 BAR (from originally 3100 BAR). The reason was that some Krags started to develop cracks. These rifles had shot maybe tens of thousands of shots with metal fatiqe on certain spots as a result. The cracks are usually found in the lower right corner, near where the locking lug engages the receiver, and in the upper left corner by the extractors supportspring. On Kongsberg Krags these corners are sharp (90`) , while the Steyr Krags have rounded corners, and are considered stronger. The sharp corner is a more likely starting point for a crack than a rounded corner.

As they say: "Allways have a competent gunsmith check any old gun before you fire it".

Faulty ammo can blow up any rifle. And this Krag blew up in the usual pattern. The cut for the extractor is the weakest spot around the case, and when it burst, this is where the gasses go. The extractor and top of the receiver ring is blown off as a result.

This link to a norwegian forum shows a Krag that were blown up on purpose. The guy loaded a full case of N110 or N340, tied it to a tree, and pulled the trigger with a string.
It looks pretty much identical to the UK incident.

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It appears the fellow needs some reloading lessons.  SEE is a possibility.  Low charge, long and perhaps rough throat.  The bullet stops for a millisecond, the powder keeps burning and pressure goes through the roof.  6.5 Swedish is notorious for this, not just in Krags, guys have blown up more than one Swedish Mauser with loads that were meant to take it easy on the old gun.

Looking at both fotos of the blown up guns I am wondering if the threaded ring did not fail first. Maybe the relatively soft barrel swelled splitting the ring and as the barrel moved forward after the ring split, the extractor pulled the rim till the rim/case failed. The American Krag is not particularly weak in the area of the cut. I just finished rebarreling an action and I was impressed with the strength in that area. The Brits may have been on to something when they mentioned the marks on the receiver. A pipe wrench applied there during rebarreling would make deep marks that would concentrate stress and drastically weaken it.

I'm not an Engineer or Metallurgist, but IMHO, this mischief was caused by extreme high pressure gases (due to over-load, under-load detonation, bullet/throat problem, compromised cartridge case???) blowing out the case head and allowing the gases to enter the action. (Metal fatigue or flaws may have contributed, but, probably not necessary or root cause).

When rimless cartridges and their rifle actions 'blow up', they look kind of similar, with top of receiver ring and extractor gone, and other wreckage somewhat restrained by wood.

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Just to set the record straight, small charges of SLOW powder in rifle cases are what cause SEE. Fast powders should be used for reduced loads (e.g., 5744, 2400 or 4759, etc.). There is a lot of misinformation out there about SEE. Anyone interested should read Firearm Pressure Factors.

At risk of appearing totally out to lunch, what is SEE?

SEE = Secondary Explosive Effect (aka - Detonation).

If I understand the basic theory correctly, there is a partial burn of the powder charge, the projectile moves forward and hesitates or hangs up, a pressure wave and intense heat occur, the remainder of the powder charge explodes creating amazing rifle shattering pressures.

I believe the most accepted culprit loads are under-loads of slow burning propellants.

(FWIW - The UK 6.5 X 55mm Norwegian Krag rifle mishap involved a load using 140 grain bullet and 34.4 grains Accurate 2520. I don't think Accurate 2520 is a slow burning propellant and 34.4 grains is a bit above the 'starting load' in some tables).

Thanks, BR.  My burn rate list says Accurate 2520 is just a smidge slower than IMR-4064 and a good bit faster than IMR-4320.  Jacketed bullet loads in the 34 to 36 grain load range have been in use since the 1930s for US Krags and the '06.  My guess is that something else was amiss.  Those case necks did not look kosher.  Bullets for a Carcano?  IIRC, those run .266-.268 and come in boxes that say 6.5 mm.

That Lee Navy makes me want to cry.  I spent the better part of 3 years trying to find a good one at a price I could afford.  I quit looking when those accidents appeared on the net.

"Slow" is relative here. The research that was done back in the '60's would indicate a SEE event can occur for powders at or slower than 3031. I wouldn't have used any of the powders mentioned here for reduced loads. There are powders specifically intended for such loads.

Butlersrangers, that Swiss blowup kind of messes with my theory. It would be interesting to see a high speed video of each of the blow ups. After the high pressure event they are not coming apart as I would have expected.
Just a couple of notes on the US Krag I just rebarreled:
The bolt did have a lot of over travel with no case in the chamber. If this is the same with a 6.5X55, the bolt could follow a severely resized case way to far.
The chamber was .010 to .012 larger than an unfired case.  Not sure if this was from an oversize reamer when the gun was first assembled or if the barrel swelled with use over the last century. If it swelled with the relatively low pressure loads then the  barrel steel is fairly soft.

If I remember correctly that Swiss rifle had a bullet sized .314.  If the chamber is like my K31, the fellow would had to have pounded on the bolt handle to get it closed.  Even so, I doubt that alone was enough to make the pressure the round delivered, likely an overload behind that too large bullet.  Not sure, but I think that fellow gave up shooting after his incident.

Would have ruined my day and probably give me the willies anytime I started pulling on a trigger for a long time after that.

I believe the K-31 Swiss mishap involved a .314" cast bullet in a .308" bore.

IIRC - The owner had some suspicion he could have thrown a double charge.

My K-31 has a .305" groove diameter.  Just shooting .308 bullets is risky.

Not with .308 sized cast bullets.  I'm close to you with a .3055 groove, .294 bore. Mine is a SIG made barrel and  I have shot my cast bullets sized .311, but found them more accurate when sized to .308.  I don't think the chamber neck is large enough to allow a case with a .314 sized bullet to chamber without banging on the handle.  Well, I guess mine would be, I just measured the neck ID on some Graf/PRVI cases that I know were full pressure, neck expanding loads, they're .315-.316.  I agree with you on .308 jacketed bullets with some K31s.  If I'd been dumb enough to jump in with near max jacketed loads that I've found online, rather than start low, work up, I imagine I'd have some pretty high pressure loads.  (Don't tell anyone, but I was that dumb once, had to pull down a bunch of rounds after getting pressure signs with the first two.)  Not rifle destroying high, but higher than I care to go.  I guess they're sorta like  US Krags, bore/groove dimensions can and do vary.  Ditto those 6.5 Swedish chambered Mausers and Krags, with the Krags generally running on the large size.

Hey guys your right about slow powders and over pressures with mild or light loads.
Do you guys remember when savage came out wth there smokeless muzzle loaders???
Well I got two of the original or ML1 which used a module to hold the 209 primer used for ignition, I knew savages PR guy at the time and I heard thru the grape vine they were going to release them and upon qestioning him he said want to work to test loads??
I was more than happy too.
Well we who were in on the beginning did about 5 years worth of R&D on different powders and there loading screen and even did pressure reads on loads.
We found some very interesting things happen, as I tell you our findings you will understand where a very reputable bullet, brass, and ammo manufacturer developed, or should I say bought the rights to a type of loading screen that give much higher velocities over standardized loads without high pressures and heat.
  Well we first started using fast powders: 5744, 4759, lil gun, 4227 in .50 cal. Gun. 4227 was listed last because it was always hard to ignite and gave poor accuracy in most guns 
  Now guys started to thinking what about slower powders ?
Well we started to look at loads for cartridge guns and trying them
Imr4198 and h4198 were tried but they were very erratic with accuracy. Loads for these were 300 grain hornady XTP's with sabot
And a favorite load of 5744 was 40-45 grains by weight. This was very accurate and recoil was light but this was the limit load wise for the faster powders but it did exactly what the inventor of this system wanted - a light recoiling muzzleloader with good killing power for his wife,nlittle did he know he had opened pandora station box!!
Well we started to look closer at what was happening??
I don't remember who did this first but they took a weighted amount of fine sugar and poured it in and then there then seated a saboteur bulle, 300 gr. XTP.  Then loaded up a 209 primer and fired it. It moved 1-1/2" to 2-1/2" up the bore !

With just the 209 primer!!!  Well we realized that the moment of ignition our chamber, the space between the saboted bullet and the breech plug was growing as the bullet began to move. Now right off we found we needed a very tight fitting sabot.  If you load smokeless powder load with a loose or light fitting sabot 99 out 100 times it will not fire.  Smokeless powder needs confinement and pressure to burn at optimum rates. I'm sure all of you have lit a pile of smokeless and watched it fizzle. We started loading bigger and bigger loads of slower powder. We found a sweet spot at about  20 % above what was a standard load. We had to compensate for the ever expanding chamber. This led us into a new direction, duplex loads !!!! Ahhhh!!! Duplex loads??? Yes, when some of the guys started using heavy loads of slower powder they noticed two pressure spikes milliseconds apart. Some actually got bulged barrels at 1-/12" to 2-1/2" in front of the saboted bullet, does that distance sound familiar??? Yeah well that's also where the second pressure spike occurred. This is where duplex get comes in.  Remember slow powders need long barrels and tight twist rifling to do their thing. What happened is for a given load of say 75 grains by weight 15 grains of that would be 4759 and the bulk 60 grains would be 4198. What this does is bring the slow powder up to optimum pressure quicker, this made for great accuracy and great velocities. No any company that recently came out with ammo in standard calibers shooting anywhere from 100 to 200 FPS without causing over pressure signs in shooting these loads???  The guy that put all this research together was a good friend of mine and I know he was selling all his info to a reputable manufacturer.  Unfortunately he passed away before I knew any more about it.
Shortly after he passed superamunition was released. I think you know who I'm talking about. Now the 30-40 krag has a long throat for the 220 gr bullet.

The krag rifles have a long throat meaning free bore that has no rifling. This space causes the two pressure spikes in a pressure reading. So a rifles ability to hold a given pressure for a given amount of time. Time being the key measure here. The bullet jumps the lead or throat of the chamber to the rifling where it now is graving into the rifling causing it to slow momentarily, thus our second pressure spike. With normal loads to loads in the high to maximum range you probably won't notice much if anything and the spikes will be close to the same pressure. Now back to time, if you try a load that is at or below standard loads the time at pressure now jumps even doubles and where is it at, right in front of the lead or free bore and the burning powder behind it now jumps to full pressure and it has a pressure wave in its way!!!
The rifle then goes boom.
SB

FredC wrote on May 19^th, 2015 at 1:35pm:

Butlersrangers, that Swiss blowup kind of messes with my theory. It would be interesting to see a high speed video of each of the blow ups. After the high pressure event they are not coming apart as I would have expected. Just a couple of notes on the US Krag I just rebarreled: The bolt did have a lot of over travel with no case in the chamber. If this is the same with a 6.5X55, the bolt could follow a severely resized case way to far. The chamber was .010 to .012 larger than an unfired case.  Not sure if this was from an oversize reamer when the gun was first assembled or if the barrel swelled with use over the last century. If it swelled with the relatively low pressure loads then the  barrel steel is fairly soft.

The steel on Norwegian Krags is like the steel used in SE Mausers.  It was probably some of the best in the world at that time.