Catastrophic failure of a Krag - food for thought

[RobD]

Interesting reading:

National Rifle Association of the UK | NRA | News | All

Rob

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[browningautorifle]

We learned years ago not to load 6.5x55 too hot when re-loading it. They aren't very forgiving. I tend to agree with their end conclusion, faulty reloading practice...and he created a bomb. Now everyone gets to second guess...

[WarPig1976]

I'll say this, you Brits don't mess around with Ka-booms.

[RobD]

The lesson for me was that this load was too light, not too hot: the case was under-filled - and probably led to detonation rather than ignition. Often spoken about - not understood, I know - but here's an example.

[browningautorifle]

detonation rather than ignition

Agreed, sounds like.

[Seaspriter]

Gentlemen, please enlighten me on what I've read in the British NRA report. It concluded: From the examination of the components parts of the failed Krag-Jorgesen rifle, serial number 32513, no definite cause of failure could be established. The evidence observed provides support to failure being as a result of a single overload event; however, the upper part of the receiver ring was not recovered after the failure and as such could not be examined. It is therefore not possible to exclude that this section of the action did contain an flaw that led to the catastrophic failure of the rifle. (this feels like a dry cough).

Your observations shed much more light on the cause of failure than the entire 11 page report. While I'm not a reloader, many of my friends are, and I'd like to warn them about shooting antique weapons (I have many myself).

The lesson for me was that this load was too light, not too hot: the case was under-filled - and probably led to detonation rather than ignition

Many of my reloader buddies talk about lighter loads to prevent over-taxing a old receiver/barrel.

Am I correct in understanding that too light a load essentially leaves airspace in the cartridge. Once the primer fires, with too light a load, instead of a normal fast burn that finishes ignition about the time the bullet exists the muzzle, the cartridge explodes, blowing in all directions, including back at the bolt and all over the receiver ring.

I think what you experts are saying is, in the Krag case cited, a combination of too light a load and a structural flaw in the receiver ring at the ejector slot blew out when the cartridge detonated (exploded). Please correct me if I got this wrong ;-)

What's disconcerting is that the Krag that blew up had been functioning flawlessly for 65 years since being rebarrelled. Structural cracks occur in metal after stresses. What's the chance of this happening in other older guns, such as Lee Enfields and Springfields, etc. ? What's the best way the owner of the Krag (or any other gun owner) could spot this problem in advance? What can an educated owner do on their own? What tests need to be done by a qualified gunsmith? How much/little constitutes "too light a load"?

This information could save someone a lot of anguish. Thanks Gentlemen.

[browningautorifle]

They make a statement that they believed reloaded ammunition was at fault, or words to that effect. I'd bet the house on it. I've seen enough reloader blow ups to full support that. Thing we always see is the reloader can't imagine what could have happened... The 6.5x55 can be cooked easily and we had people changing the shape of their bolt face in small ring Mauser while blowing up AG42b rifles... That's a cartridge you need to be careful and pay attention. Yes, airspace can do it, wrong powder can do it...many things can do it. I saw the report as all over the place so as to leave ambiguity and clouds.

[Badger]

Here's the document for viewing in-line with thread, to make it easier to view for members ...

Regards,
Doug

---------------IF THE PDF IS BLANK CLICK HERE TO VIEW.---------------

[jmoore]

Points 30 and 31 on page ten I find particularly valuable as to failure mode of the receiver. Instigated by the overpressure event, which was well above the UTS of the brass. The brass flowed outward, working against normally non-load bearing areas. Would not at all be surprised that there were pre-existing cracks in the unrecovered parts of the receiver ring, base on the evidence given!


Educational upside to this incident is that the bolt lug wasn't sheared.

[BMF]

Seaspriter: 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.

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.

Kammeret.no Se emne - Hvordan ryker en Krag Jørgensen?