Not a great way to begin a thread on load development but....

[Eagle1899]

Exploring the "wrong diameter bullet in the box" theory. If a larger bullet was loaded into the case then chambered, it would most likely push back into the case raising pressure or not give any neck clearance. Enough pressure to see the destruction in the pictures. I don't know.

 

[Cloudrepair]

A close up picture of the cracks would be helpful. Of the metal of the cracks . The metal in part of the crack looks a different color that tells me an existing crack.

 

[Kracken McGraw]

To me basically all one can do is move on and be very thankful that you weren’t injured. My superstition’s would move me away from that brand of rifle, brass, and cartridge.

 

[Doom]

Having the action tested isn't a bad idea but without filing a legal action you are extremely unlikely to get the information from Christensen as to the specification. It is considered Intellectual Property. Since no one was injured you're not likely to get anything more than a new rifle. As has been noted the warranty is void.

To the OP, since you saw an increase in velocity for this rifle and you eliminate a powder issue and all other components are the same lot, you might concentrate on anything you did with the rifle between sessions.

Seldom is it obvious exactly what causes these failures. There really too many things that can cause it and not enough evidence to narrow it down. Yep, sometimes we do find the odd wrong powder or a double charge possibility. If the action did crack the manufacturer probably has MPI (mag particle inspection) inspection showing no issues and the rifle likely was tested with 3 or more proof loads of at least 87KSI.

 

[swd]

---
is it possible? you "LIGHT" charged one by accident
powder measure started running low and didnt catch it?
and a flashover happened over the whole powder charge
---

This is something that can definitely cause a blowup like this. It was well documented with the 243 Win and 4831 back in the 60's after a few 243's got blow up.

A question for the OP do you recall if was there any hesitation, even a nano second that might not have felt quite right when you pulled the trigger?

 

[DShortt]

I haven't read every reply but I have an example of this kind of failure in the shop. This was caused by extremely high pressure. Notice in this case the part of the cartridge case that's missing as well as the copper wash extending down the action. The failure points are exactly as happened here. I know what happened in my case although I don't think it's relative here. In my case it was using incorrect powder causing catastrophic case failure from extremely high pressure. Here pressure was high enough that escaping gas cut steel as passed down the bolt in the extractor slot. We estimated the pressure to be around 110,000 to 120,000 PSI. The pressure shock wave from a violently expanding barrel tenon gets transferred to the receiver along with the pressure of the escaping gas and you can see the failure points. The odd thing in my case was the barrel was not deformed at all. The expansion of the tenon did not exceed the yield point of the steel. I head spaced it on another action and it performed perfectly.

I understand that assessment. The only thing that contradicts that assessment is, why is the barrel still intact and why is there a 'button' of brass at the ejector hole location? I only know of a few causes of excessive bolt thrust. I freely admit, I definitely do not know everything.

I do not disagree with your assessment. I'm merely trying to make that explanation align with my understanding of over-pressure events.

Still looks like excessive bolt thrust to me based on my understanding of things, hence, my question.

 

[Steve Donlon]

This is scary
I will throw something out there that happened to me once
Albeit I was using some "Seconds" bullets Blems, or whatever
Anyway, loading for an AR15 and just plinking rounds nothing extreme
Suddenly I felt an immense concussion of harsh recoil and my Magazine ruptured and shot out of the bottom of the magwell
I was beside myself, there was no way I used an overcharge, or the wrong powder because the previous rounds were the same exact charge and powder 26.0 grns of W-748 / 50 grn bullets
---
It really didnt hurt the rifle much but bent the extractor
Kinda hurt my hand a little, lol like firing a 500 S&W
I kept looking for further causes
Of course when I looked through the bore and saw light at the end
I dismissed an obstruction as the cause
---
Still could not find a reason
So I went to run a rod through the bore to maybe feel for something weird
I found something weird
The core on one round, had shot out, as if the base of the bullet blew out
The jacket got stuck in the bore which is relatively thin, so hard to see halfway down the bore
When the jacket stuck, the next round fired hit that jacket and caused major overpressure
I had to beat the stuck jacket out with a Dewey rod
You might inspect the bore more for something like that
or if it did happen, both obstructions could have shot out
Im lucky I was able to find the cause
I dont use "Seconds" bullets anymore

I have seen the same thing happen in an AR with a carbon ring. In the AR the bottom half of the case was welded to the extractor and locked up with the magazine blown to pieces in a 300BLK with much less powder than a 280AI

 

[DaveTooley]

I understand that assessment. The only thing that contradicts that assessment is, why is the barrel still intact and why is there a 'button' of brass at the ejector hole location? I only know of a few causes of excessive bolt thrust. I freely admit, I definitely do not know everything.

I do not disagree with your assessment. I'm merely trying to make that explanation align with my understanding of over-pressure events.

Still looks like excessive bolt thrust to me based on my understanding of things, hence, my question.

Oh I'm sure there was excessive bolt thrust but the question is when and what effect did it have on the outcome. What sequence did all this happen. Interestingly I've had other high pressure events where the case didn't rupture (non Sako or M16 extractors) and the tenon and bolt nose were expanded but the receivers stayed together. On the action I have here there's no deformation of the action lugs or bolt lugs.

Here's my guess of the sequence of events.
Pressure spikes expanding the tenon, sending a shock wave/ load to the receiver.
Almost simultaneously the case ruptures releasing high pressure gas into the area around the lug area.
Increasing the load on the receiver. I think both put a load on the receiver at the same time. A double whammy.
Bolt thrust goes up. But how does that contribute to the radial load on the receiver?
Next the receiver splits.

You can see the brass flowed and formed a belt in the counterbore and flowed into the ejector pin hole. My guess it shows how far below the bolt face the ejector can travel.

 

[tdogg]

Wow! That is scary! Glad you are unharmed!

Please post up if you ever get a solid resolution to this catastrophic failure!

I have a hard time believing it wasn't a barrel obstruction. It would be interesting to know if the barrel is bulged somewhere.

Toby

 

[DShortt]

Oh I'm sure there was excessive bolt thrust but the question is when and what effect did it have on the outcome. What sequence did all this happen. Interestingly I've had other high pressure events where the case didn't rupture (non Sako or M16 extractors) and the tenon and bolt nose were expanded but the receivers stayed together. On the action I have here there's no deformation of the action lugs or bolt lugs.

Here's my guess of the sequence of events.
Pressure spikes expanding the tenon, sending a shock wave/ load to the receiver.
Almost simultaneously the case ruptures releasing high pressure gas into the area around the lug area.
Increasing the load on the receiver. I think both put a load on the receiver at the same time. A double whammy.
Bolt thrust goes up. But how does that contribute to the radial load on the receiver?
Next the receiver splits.

You can see the brass flowed and formed a belt in the counterbore and flowed into the ejector pin hole. My guess it shows how far below the bolt face the ejector can travel.

Thanks for your thoughts. I appreciate it more than you know.

I'll continue to 'mull this over'. I'm a big believer in indirect thinking.

 

[searcher]

This is something that can definitely cause a blowup like this. It was well documented with the 243 Win and 4831 back in the 60's after a few 243's got blow up.

A question for the OP do you recall if was there any hesitation, even a nano second that might not have felt quite right when you pulled the trigger?

I agree, though he was, as I read it, well above his starting load when this occurred. Pre-detonation would have most likely occurred at the lower charge settings. I have experienced that occurrence in both my .375 H&H Mag and my 7 MM Rem Mag, both times shooting light bullets with low charges. In the .375, it was using a published load from the bullet manufacturer. Both resulted in huge recoil but no damage or injury. In such situations, there is a very small, but noticeably longer time elapse between pulling the trigger and felt recoil from ignition. I had always been very leery of using slow powder and light bullets in my .243 due to those warnings in the reloading manuals.

 

[ELR LVR]

In a way, I'm thinking the action did as designed to prevent harm to the user
and spit the barrel forward.
better than a Bolt getting shot through your head by shearing the lugs if it stayed together
---
still not discounting the action may have also failed though from improper heat treat

 

[Mike Powers]

What's the possibility of the barrel nut loosening? I see lots of parts but not the barrel nut.
Mike

 

[DShortt]

What's the possibility of the barrel nut loosening? I see lots of parts but not the barrel nut.
Mike

Probably because this design is a barrel shoulder snug against the action/lug and no barrel nut involved.
Look at the barrel and the lug. There is a shoulder there.

In the past, I mistakenly did not torque the barrel correctly and it came loose. It didn't blow apart the action. Accuracy just deteriorated.

 

[Mike Powers]

Possible incorrect recoil lug thickness
Mike

 

[DShortt]

Possible incorrect recoil lug thickness
Mike

Huh?

This was a factoy rifle according to the OP.

It has a shouldered barrel.

Multiple prior rounds fired without incident.

If the recoil lug was changed, that might cause a headspace issue. It wouldn't cause the action to split apart.

Oy!

 

[swd]

I agree, though he was, as I read it, well above his starting load when this occurred. Pre-detonation would have most likely occurred at the lower charge settings. I have experienced that occurrence in both my .375 H&H Mag and my 7 MM Rem Mag, both times shooting light bullets with low charges. In the .375, it was using a published load from the bullet manufacturer. Both resulted in huge recoil but no damage or injury. In such situations, there is a very small, but noticeably longer time elapse between pulling the trigger and felt recoil from ignition. I had always been very leery of using slow powder and light bullets in my .243 due to those warnings in the reloading manuals.

I was thinking more there was possibly a mistake made on the one round.

 

[GAnderson]

Could there be a possibility that the bolts got switched between your rifle and your son's rifle? This could have resulted in the excessive bolt thrust theory that some have suggested. Most bolts are serial numbered to the action...maybe check to see if this might be the case.

 

[ELR LVR]

Could there be a possibility that the bolts got switched between your rifle and your son's rifle? This could have resulted in the excessive bolt thrust theory that some have suggested. Most bolts are serial numbered to the action...maybe check to see if this might be the case.

Confused, hows that blow up an action?
Unless you mean due to it
excessive headspace happened, even then, i've had plenty of case head seperations in rifles up to 7mm Mag and never had anything like this happen
However, my bolts are vented should something like over pressure or pierced primer happens and the pressure vents out the side of the bolt
maybe his bolt was not vented?
---
Different Bolt : how do we buy PTG aftermarket bolts and put them in our guns? which is a different bolt
---
OP, is your Bolt Vented?

 

[DShortt]

I was thinking more there was possibly a mistake made on the one round.

The weird thing about SEE is, it's not something that can be easily replicated.
It's an 'alignment of the stars' thing at best.
So, I tend to believe that all manner of reloading mistakes get lumped into this category when no obvious explanation exists.
Perhaps this was a case failure. If so, it was a one- off case. Perhaps this was an overcharge. Given that the barrel would have to contain that excessive pressure and not the action, I'm not sold on that idea.
Unless something was involved that we've not been told, it will remain a topic of opinion and never 'resolved'.