Blown up Krag in England -- comprehensive report

[Dutchman]

(http://www.nra.org.uk/common/files/news/15/KJ-Redacted-report-complete-v2.pdf)http://www.nra.org.uk/common/files/news/15/KJ-Redacted-report-complete-v2.pdf

Krag-Jorgensen Safety Update
The NRA recently completed, on behalf of MoD, an investigation into an accident involving a Krag-Jorgensen rifle. The technical investigation revealed matters that the NRA believes should be brought to the attention of all owners of Krag-Jorgensen rifles. In particular, there is published information that a substantial number of K-R rifles were rebarreled shortly after World War II, and that the standard of work may have been unsatisfactory in some cases.
Aspects of the technical investigation into the rifle involved in the accident tend to confirm that information. Please see the attached redacted version of the accident report including the full detail of the findings regarding the rifle itself.
The NRA requires all members owning Krag-Jorgenson rifles fitted with replacement barrels (other than those replacements carried out under the current owner?s instructions and bearing proof marks issued under CIP regulations or by one of the UK proof houses) to have the rifle checked by a competent gunsmith before it is used under the auspices of the NRA

Andrew Mercer
Secretary General

Click here (http://www.nra.org.uk/common/files/news/15/KJ-Redacted-report-complete-v2.pdf)to download and view the redacted report version 2




Updated: 07-May-15 (Original posting: 07-May-15)


(http://www.nra.org.uk/common/files/news/15/KJ-Redacted-report-complete-v2.pdf)

[cuzinbruce]

Interesting post. I note that it was a Norwegian Krag. Hope they weren't hurt badly.

[303Guy]

Wow. Well, the bolt itself held up well.

Looking at the dodgy reloads I wonder whether that case neck was too long and needed trimming. Could it possibly have jammed into the throat taper and caused the over pressure event? The fact that some necks were deformed and some shoulders pushed back is suspicious. I didn't think A 2520 was a slow powder? Was the load used a published one? Well I suppose I can look for myself but I don't have too many loading manuals.

Nothing on A 2520 but Varget can go down to 34gr under a heavier bullet.

[JeffinNZ]

Awesome report. It's a great shame it was required.

[MtGun44]

Is that the US NRA or is there a British organization by the same initials?

OK, the pdf finally opened and I see it is the British NRA, which makes sense.

Thorough report. The recut, modified thread form was fairly scary.

Bill

[smokeywolf]

Couldn't get either link to open.

[Ballistics in Scotland]

It is an impressive report, and fortunately it sounds like the injuries weren't severe.

Those marks on the first thread of the receiver are puzzling, and it seems possible that they had started cracks, which may been worse in the missing upper fragment. My guess is that the previous barrel was an extremely tight fit, which someone couldn't get out. So he cut it off short and bored it out. That is normally a sensible enough way to go, but lacking proper equipment to reduced the stub almost to the spiral that was in the V-threads themselves, he finally had to punch or chisel the pieces that were left in the threads. He would probably have been better off with a black powder firearm which didn't have to be hardened at all, but the report raises, though it doesn't settle, the possibility that the steel was somewhat brittle from manufacture.

We then have two possible contributing factors, as accidents usually happen from a combination of factors, each of which you would have got away with on its own. One may have been some peculiar practice in brass forming. One possibility is that he neck-sized his cases in a 6mm. or .257 die, probably through some bizarre quirk of the intellectual processes, since the right 6.5x55 is commonly available in the UK.

The other factor may have been the occasional freak high pressure which results from a case partly filled with slow powder, although this wasn't an extreme case of such a condition. The report rightly says this isn't yet fully understood, although informed opinion seems to lie on the side of a pressure wave having some free movement before it encounters the bullet. It is a pity it has come to be called detonation, since it appears not to be detonation as explosives engineers define it, the explosion proceeding as the percussive wave-front passes through the grain.

The interesting thing is that the bolt, as in almost all rifle explosions, hasn't been blown out of the rifle. Rearward ejection of the bolt is what people intuitively fear with the bolt action, and especially with the Krag, and its apparently weak locking lug. The report appears to cast no discredit on the Krag as usually constituted.

[dromia]

I have to say I found that report to be wanting in many respects when it came out and I am disappointed that the NRA couldn't do better.

[13Echo]

The US Krag front locking lug has a reputation of cracking. Not a desirable occurrence, however, even if it sheers off the large guide rib serves admirably as a safety lug and will prevent the bolt being blown from the rifle. Michael Petrov did a series of tests with a Krag with no front locking lug and finally managed to blow it up but the bolt stayed in the action. the Krag's reputation of weakness stems more from its brittleness from the heat treatment it received than it's design.

[leadman]

I use AA2520 and it is in the same burning rate with H4895 or IMR 4064. Not really a "slow" powder. Sounds more like a marginal job of rebarreling and poor reloading practices.
Hope the injuries were not too terrible.

[oldcanadice]

The Norwegian Krag is a great and strong action. It differs significantly from the US action in the type of steel used and far better heat treatment. The actions were also set up so that the side lug was bearing when a cartridge was chambered, so the bolt was actually two-lugged -- the lugs were just offset. Given the length of the side lug, I can't imagine the bolt ever coming out of the rifle. Inches of steel would have to move to get it done.

In recognition of the action's strength, the European 6.5x55 cartridge that it uses is (or at least was) commonly loaded by Norma to working pressures of 48,000CUP. I have an old letter from Nils Kvale of Norma indicating that fact.

Regarding the ammo, the guy may not have been a jerk. To me it looks like he was forming an external donut to take out all of the headspace slop as he closed the bolt, a stunt similar to long-seating a bullet when trying to blow out a case to fit an Ackley chamber or trying to lengthen good cases that had inadvertently been sized too short. The low charge of powder also seems to indicate something like that. Given the expense of components over the pond, that may have been a deliberate attempt at salvaging cases.

I agree the investigation seems perfunctory. I'd also guess that, if he lived, the guy will never use his forward holding arm again.

Bottom Line: Listen to the powder makers. Do NOT short-load slow-burning powders into low-density situations.

[Larry Gibson]

Classic SEE, no doubt about it.

Worn barrel with probable throat erosian from use over the years.

Long throat.

Reduced load (60% load density) of harder to ignite ball powder.

Fourth shot in series.

Evident extremely high pressure during event.

Classic SEE destruction of the action.

Larry Gibson

[Ballistics in Scotland]

John J. Donnelly gives the volume of the 6.5x55 case as 3.56ml., and the inch figure in my Load from a Disk program converts to 3.62ml. Neither differs significantly from the 3.68 quoted in the report. But those are volumes to the case neck, and as an initial combustion space are reduced by the insertion of the bullet. A little further on the report explains how powder to 60% of that volume translates to what shooters would call a 75% load. This gives much less likelihood than 60% of something untoward happening, unless it is conjoined with something else, or the amount or nature of the powder in the disastrous round was quite different.

Throat erosion is just conjecture, and seems unlikely to be a source of accidents of this type. Overused machinegun barrels can actually produce an egg-shaped cavity, and while it was an old barrel, British target rifle shooting seldom involves the rapid or lengthy fire which gets a target weight barrel really hot.

I think the report is an extremely good one, limited by the information available. In particular the missing top of the receiver ring removes the chance of establishing whether cracks were begun by the suggested use of a punch or screwdriver blade. That part of the receiver was unimpeded by wood, and if it has come to earth yet it may be a long way away.

Such an accident can indeed cause severe injury or even death, but no mention of either is made. It is more common for rifle and shotgun explosins to result in light injuries or none at all. It is to be hoped that those in this incident fall under this category.

[frnkeore]

Such an accident can indeed cause severe injury or even death, but no mention of either is made. It is more common for rifle and shotgun explosins to result in light injuries or none at all. It is to be hoped that those in this incident fall under this category.

The report implys that the injurys where sever, in that they didn't want to wait for a ambulance and that two of the three men were admitted into hospital and the other treated as a out patient.

What I believe caused the event is, the receiver ring failed and the barrel blew out of it.

It looks to me like there is at least one old crack. Note that the case is still in the barrel and with that, the only escaping gas was from the primer pocket. It may have been a over charge that started the event but, it certainly was not a SEE. With that much powder, it would have spilt the barrel and blown the case out of the barrel.

The case that still in the chamber is the clue, not even the case head blew out.

Frank

[Ballistics in Scotland]

Severity of the injuries is really a bit of a red herring in this case, since we know that accidents of this kind can cause anything from instant death to being totally unhurt, and neither say a thing about who or what was to blame. I took the report as implying that the men didn't need to be lying down or splinted. It is a sobering thought, though, that in hearing of such cases, a lot of us want them to have been severe.

[Larry Gibson]

The report states the fractures were from a high pressure even as was the blown primer pocket. The receiver cracking and the barrel would not have caused that, especially the blown primer pocket.

The throat erosian was indeed "conjecture". It was based on 45 years experience shooting several 6.5x55s a lot, including shooting out three 6.5 barrels. Given the age of the barrel in question and when it was installed throat erosian is probable. All of the factors for an SEE are present in tis event including the resulting damage to the rifle.

Larry Gibson

[frnkeore]

The pressure, can not get to the receiver ring, w/o the barrel expanding beyond it yield strenght. The barrel looks in tack w/o any swelling and the case head does not look swollen either. Look closely.

IMO, the threads failed, because of a pre-existing crack (look at the color difference in the crack in photo #4). The receiver ring opened, the barrel moved forward. The primer came loose, allowing the escaping gas to accelerate the axle movement and that created a impact moment against the threads, shattering the receiver ring, radially.

Frank

[Ballistics in Scotland]

Yes, that is what it looks like to me. No doubt there was excessive pressure, but the most likely explanation is that the receiver ring failed, possibly through damage in the barrel change, and the barrel got away from the bolt.

[Uncle R.]

Sequence is everything.
The barrel is very nearly intact, so it seems logical that the receiver ring did not fail from excessive radial pressure.
Did the case head fail first, allowing high pressure gas into the receiver ring causing it to burst?
Or did the receiver ring fail first, allowing the barrel to move forward and the case head to blow from lack of support?
<
I'd put my money on option two. That receiver ring appears to have pretty much shattered. Kinda reminds me of an early Springfield receiver failure, and I suspect for the same reasons. Even if the case head blew out first I'd expect better containment from a receiver ring, and not brittle shattering. The buggered threads probably didn't help, and if they're indicative of the quality of workmanship for that barrel replacement I wouldn't be surprised to learn that receiver had been cracked at that time and the crack had gradually spread until failure.

I'm fairly confident a real metallurgist could determine the facts and probable cause if allowed to examine the pieces and make a few tests. I'm with Dromia in that I think the "investigation" fell far below what I'd consider a professional level.

Uncle R.

Well - looks like I wasn't the first to arrive at these conclusions. My apologies to and agreement with the two posts above mine.

Uncle R.

[Outpost75]

This reinforces the admonition not to reduce any spheroidal rifle powder below 85% of case capacity.

[13Echo]

Looking at the pictures it is obvious that the case head is expanded as is the primer pocket from excessive pressure. When it blew it ruptured at the extractor, the weak spot in the breaching and that took out the receiver ring which is not supported by the barrel at that point. The barrel would not have to fail to produce this receiver ring failure. The rifle does look like it has suffered the attentions of Mylo Farkenparker (or is it Parkenfarker?) the famous shadetree gunsmith and part time farrier which appears to have greatly contributed to the failure. Figure 8b shows what appears to be rust in the fractured metal which suggests a preexisting fracture of the receiver. The cause of this accident appears to me to be multifactoral resulting from a combination of shadetree gunsmithing and improper loading.

[John Boy]

Is that the US NRA or is there a British organization by the same initials?
The next comprehensive like this one from the US NRA ... Will be The First One!

[303Guy]

When it blew it ruptured at the extractor, the weak spot in the breaching and that took out the receiver ring which is not supported by the barrel at that point.
I agree with 13Echo. One thing to remember is that once the case has ruptured, the escaping gasses have a very large surface area to act on and that is what blows the receiver ring. This rifle shows a portion of the extractor cutout failing. That would be high pressure but that pressure was directed out the failure point. The position of the stuck case indicates that there was no headspace issue with the rifle as is stated in the report.

The crack with what appears to be rust on it was described as having had brass condensing onto it during the event.

That action may or may not have lost its receiver ring had the threads not been butchered but ruptured cases are known to blow good actions. Like firing a 308 cartridge in a 270 chamber. In one such incident the barrel blew halfway to the target (indoor rifle test range). The barrel was still serviceable! Not so much the action which had split its receiver ring. Other 270's survive such abuse!

[GSM]

Is there a good link to the non-redacted report? Both links in the OP point to a redacted version.

Thanks.

[dromia]

That is one of the many flaws of this "report"/"investigation", the redacted parts. Private information like names I can understand but there is information germane to the event that have been removed for no apparent good reason.

This is the public version I have been unable to find a non redacted version.

[Silfield]

About a month ago I posted the very same link that the OP posted but on a Canadian shooters forum as I know a few Krag shooters north of the border.
Within minutes I was called a scaremongering idiot (amongst other things!) and then the Brit baiting trolls started :shock:. There seem to be a good amount of young (my guess), irrational keyboard warrior types up there!
Refreshing to see that it has been posted on here and has been debated with rationale and logic. I was under the impression that, regardless of where we come from, we should all look after each others backs if possible.

:castmine:

[Ballistics in Scotland]

That is why they redact things. Apart from names and information that could identify them, they remove opinions that could give rise to a lawsuit and become evidence in it.

I didn't see rust in any crack, and the supposed brass deposits are far from conclusive, or meant to be. It may be that there was much clearer evidence of an old crack in the missing receiver ring top. If there was, it could easily result in the fractures we see on the sides, even if no crack had begun there.

There are two advantages to square threads in barrel fitting.

If you press down and try to turn a 120 degree cone in a matching socket, friction will be high. That is very like what a 60 degree thread is, only it is wound around a cylindrical body. A square thread, like a flat-ended cylinder in a matching socket, gives much less friction. This is used in two ways. A coarse pitch square thread, in a fly-press for example, will not seize, and is easily reversible. A fine pitch square thread, as in a rifle barrel, applies more of the gunsmith's force on the wrench to drawing the barrel tight against the action face.


The other factor is that by the spiral surface of the v-thread longitudinal force on the barrel tends to exert an outward force on the receiver ring. A square thread doesn't do this. It isn't uncommon to find or perhaps create cracks in rebarrelling of the square-threaded M1917 and P14 US Enfields. But people appear to get away with this more often than I'd like to count on in the V-threaded old heat treatment 1903 Springfields.

There was clearly massive gas escape, but it didn't necessarily precede failure of the ring.

[Ballistics in Scotland]

About a month ago I posted the very same link that the OP posted but on a Canadian shooters forum as I know a few Krag shooters north of the border.
Within minutes I was called a scaremongering idiot (amongst other things!) and then the Brit baiting trolls started :shock:. There seem to be a good amount of young (my guess), irrational keyboard warrior types up there!
Refreshing to see that it has been posted on here and has been debated with rationale and logic. I was under the impression that, regardless of where we come from, we should all look after each others backs if possible.

:castmine:

Yes, it seems quite a different environment from Australia, although that is not a land of repressed self-expression. Perhaps Canadians feel in danger of subservience to some other nation they can't afford to bait. The fact is that the accident happened as they do in every country, and other shooters have a pardonable interest in not being killed or injured. So an inquiry was the right thing to do, and a good inquiry allows the available information to have some bearing on its findings. In this case the evidence wasn't enough to be totally conclusive. The alternative is to make up an explanation, as perhaps those board members did. They may not make old bones... if they get to shoot a real gun, of course.

[BMF]

Hello

This is an interesting discussion. The Krag in the report blew up in the typical manner. When gasses get loose from a burst case, blown primer etc., it's the cut out for the extractor wich is the weak spot. Here's a link to a norwegian forum with pics of a Krag that were blown up on purpose. It looks almost identical.
http://www.kammeret.no/forum/viewtopic.php?f=14&t=86653&sid=debd5878d18e0e7b53e76942bd577055&start=80

We also discussed this incident on the Krag forum a while back. I did write some about incidents in Norway there.
http://forums.gunboards.com/showthread.php?398381-Krag-blow-up-in-Britain-Report-now-published

[303Guy]

Welcome aboard BMF​.:drinks:

[leadman]

According to the Accurate website 2520 is a medium burning powder with use in the 308 Winchester for target use. My personal use of this powder confirms this.
I did not find a listing on various companies for this powder in the 6.5X55 but I did find it listed for the 7.65X53 Arg. With a 150gr bullet the start load is 41.9grs which is more than the 34grs approx that the shooter had loaded. I do have 2 Accurate load manuals I will try to check in tomorrow.
Even though 2520 is a medium powder it is close to the listing for slow powders.
Not sure this is the cause but it seems to be the shooter loaded well outside of any listed data.

[madsenshooter]

I'm with Larry, classic case of SEE in a chambering well known for it. Can't agree with the 1950s idea of flashover being behind SEE with low doses of powder, got to remember those Weatherbys had long throats too. (Info found in one of the links)

[303Guy]

You don't think the appearance of the loaded cartridges and the comment made on them suggest poor loading practices? I wonder whether the neck was simply too long and it jammed the bullet in the throat. Irregular over-length necks could explain the expanded shoulders on some loaded rounds.

[Larry Gibson]

Certanly do agree that it was "poor loading practices" at was the root reason the SEE occured. The poor choice of a lower than recommended powder charge and the choice of powder in that cartidge in that rifle set the stage for the SEE. "Poor loadng practices" encompases the thought process and decisions on the components to use as well as the mechanical process and the end product.

The "poor loading practices" was the reason for the SEE, the occurance of the SEE was the cause of the destruction of the rifle.

Larry Gibson