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

[dellet]

Look at the bolt face.

It is cracked at the ejector. The case head has literally extruded into the ejector hole. The ejector is stuck in the cavity. The firing pin appears to be stuck in the bolt body.
Yes, the extractor blew out and the case head failed as a result.

I still don't see an explanation for overpressure.

I see a lot to explain excessive bolt thrust.

And I'm aware of a short list of causes.

A contaminated case body ranking very high on that short list.

Lesson here?

Make sure your case bodies are clean and dry if you choose to run high pressure loadings.

You can have excessive bolt thrust without excessive pressure. Just add oil or water.

It’s really hard to blow a bottom plate out of a stock with bolt thrust alone. That takes excessive pressure, and a lot of it, someplace it’s not supposed to be.

Of course there was excessive thrust, but the thrust did not blow the bottom plate out. That was gas pressure. Just like the case head did not fail extruding into the ejector hole. The case failed due to internal pressure blowing it out the weakest point on the bolt. Thrust did not push it out.

Consider that the bullet was clocked at relatively normal speeds after blowing a 50 caliber relief port behind it. That’s some serious pressure.

 

[shoot4fun]

A few years back someone posted pics of a Savage 338LM they had detonate on them. Fortunately, their injuries were minor. There were probably 40 posts theorizing everything under the sun as the cause. The blame went from manufacturer to reload to some really far out reasoning for the issue. I took one look at the picture and saw the obvious. There was a cleaning rod handle at the muzzle end of the barrel.
I asked if the rod had somehow found its way into the barrel before the rifle was fired and, sure enough, the OP explained fired brass was sticking in the chamber so he was using a cleaning rod to bump it out. He simply got distracted and forgot to remove the cleaning rod. The end result looked very much like the OP's rifle here. He said there was a velocity recorded for the previous round so the bullet had to leave the barrel and the round that blew the rifle up also recorded. I believe this to be an over pressure issue but it will be very difficult to explain what happened.
Previously I stated the issue was related to ammo, brass being Peterson with less internal volume and load/bullet combination being above limits the action or brass could tolerate.

 

[Bottom Fodder]

Pressure like other things follows the path of least resistance, to me that path was rearwards not forwards. But why on only this one round ?
My thinking is this, the damage started with the other rounds for what ever reason and grew with each firing this one round was the straw that broke the camels back.

 

[DShortt]

You can have excessive bolt thrust without excessive pressure. Just add oil or water.

It’s really hard to blow a bottom plate out of a stock with bolt thrust alone. That takes excessive pressure, and a lot of it, someplace it’s not supposed to be.

Of course there was excessive thrust, but the thrust did not blow the bottom plate out. That was gas pressure. Just like the case head did not fail extruding into the ejector hole. The case failed due to internal pressure blowing it out the weakest point on the bolt. Thrust did not push it out.

Consider that the bullet was clocked at relatively normal speeds after blowing a 50 caliber relief port behind it. That’s some serious pressure.

Was it really that much overpressure, or just the normal sequence of events when a case isn't clean and fired at high level pressures?

I don't have the financial resources nor the inclination to destroy multiple firearms to establish a baseline.

Again, you all believe whatever you wish. I'll rely on what I see with my eyes.

 

[tominboise]

Regarding your reloads, how full is the case with this powder charge? If there was some small foreign object in the new case as you pulled it from the box, would your powder charge level have overflowed out of the case neck? Something like a primer inside the case.

 

[Clabdor]

1. Stainless steel receiver or titanium?
Heat treated steel receiver failed, when not done correctly. (Sako & Tikka rifles. 2004)
2. Brass trim length to long. Crimped bullet in chamber. Seen & inspected the reloads. M70 locked. Stock split.

3. Some fancy powder thrower measures may have leftover pistol powder still in measure. When not cleaned fully.

4. Proof loads run at 93,000 PSI and dont take rifles apart.

Note- H4831 has a 10% different from slowest to fastest lots. This will not blow up rifles. https://apps.dtic.mil/sti/citations/ADA572333

1 - I assume SS but I don't know for sure.
2 - Brass was factory. Brass was virgin - never shot
3- I don't reload pistols. I fully clean the charge master every time. No residue because I use different powders for my different calibers.
4. Good to know. Not sure I understand the reference.

 

[ELR LVR]

You can have excessive bolt thrust without excessive pressure. Just add oil or water.

It’s really hard to blow a bottom plate out of a stock with bolt thrust alone. That takes excessive pressure, and a lot of it, someplace it’s not supposed to be.

Precisely !!!
an extra 900lbs or so of bolt thrust wont split an action apart like that
An issue like this requires thinking in the terms of Physics regarding fluid dynamics
*** Hydraulic pressure
NOT --- air pressure
---
at those pressures compressed gasses act like a fluid (non compressible)
---
Could flashole diameter have caused such an overpressure event?
be it too large or too small?
Igniting the whole powder charge all at once? (Fault of the brass flash hole diameter?)

 

[Clabdor]

I see some primer cratering, but no primer "Flattening"
Signs of being at the upper limit
but not excessive
---
I see no shiny Ejector marks on the rim
---
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
---
I've ran low before and didnt catch it and then had to go back and weigh like 100 cases to find the 2 light ones

I double weigh each charge load on separate scales. Additionally, I had two more rounds at the 57.4 weight which I didn't fire. I pulled the bullets out of those rounds, weighed the powder and it was 57.4 in each. Is it possible that the one I fired was "light". Since I double weigh them and the others in that string were accurate, I would find it possible, but not highly probable.

 

[Clabdor]

Heat treat fail?

Titanium rifle receivers, commonly made from Grade 5 (Ti-6Al-4V), require specialized heat treatment to optimize strength, fatigue resistance, and durability, often reaching hardness levels of 30-40 HRC.

Yea...don't know.

 

[ELR LVR]

I double weigh each charge load on separate scales. Additionally, I had two more rounds at the 57.4 weight which I didn't fire. I pulled the bullets out of those rounds, weighed the powder and it was 57.4 in each. Is it possible that the one I fired was "light". Since I double weigh them and the others in that string were accurate, I would find it possible, but not highly probable.

I am def seeing this was likely not your fault, albeit, a very unfortunate happening which is hard to find who or what is at fault.
but it kinda scares the crap out of me considering my own loading practices are as careful as your own and that this happened at all

 

[Clabdor]

I concur with this. In looking a your fired brass, I do see rather heavy cratering of the primers on that one set of rounds of 5 in a row. If you were way over pressure though the next thing I would expect to see are very flat primers or blown primers and perhaps smearing due to heavy bolt lift. This looks like a case failure. The only thing I can think of would be defective brass or a barrel obstruction like a jacket lost and left in the bore. I've only lost jackets after the bullet left the barrel however.

If something was left in the barrel I just don't understand how we would have registered velocity and impact downrange on target. What would have been left?

 

[Clabdor]

Thank the Good Lord no one was hurt.
Since I am only looking at pictures I can only speculate as to what happened. Also although I am a mechanical engineer by trade most of my work was on power plants (at much lower pressures) so I really can’t profess to be an expert on the mechanics of rifle actions.
Looking at the cases from your previously fired rounds I don’t see any signs of overpressure. Since you were reloading with only one powder and one type of bullet it is unlikely that the wrong powder, or wrong bullet was the cause. Since the previous bullet showed up on the chronograph and impacted on the target it is unlikely that the barrel was obstructed. Especially since you could see down the barrel after the final shot. The fact that the bore was clear and you got a reading on the final shot tells me the bullet left the barrel. What I found quite odd was that the second to last shot registered approximately 2800 and the final shot 2600 and yet the action let go. I did a quick check on Gordon’s Reloading Tool and even if the powder charge was slightly off, say 1/2 to one grain higher, it seems that you would still be in a safe range that certainly shouldn’t destroy an action.
The other thing I find odd is that bolt thrust is generally straight back against the action lugs yet this doesn’t seem to be how the action failed. Outward thrust from the brass case is normally against the barrel chamber walls and constrained by the barrel itself and yet it doesn’t seem as if the barrel is bulged. You might want to take some micrometer readings on the barrel to confirm it is not bulged. The way the receiver failed it almost strikes me as if the case failed first releasing the expanding gasses between the bolt and the action splitting the action apart the way it did. Yet the problem with this theory is that the venting holes in the sides of the receiver should have vented the escaping gasses limiting the pressure rise. Even normal chamber pressures in the 55,000 psi range is probably more than enough to do serious damage if defective components fail.

I'll check the barrel but I'd have to get a print of the original barrel so I can see where it could possibly deviate. I would hope that receiver had venting holes, but I'd have to call CA to find out. I'll call CA this week.

 

[Clabdor]

Regarding your reloads, how full is the case with this powder charge? If there was some small foreign object in the new case as you pulled it from the box, would your powder charge level have overflowed out of the case neck? Something like a primer inside the case.

The powder fill on these cases wasn't full. I considered that I had a compressed load, but I certainly didn't notice anything to that affect during the loading process.

 

[Clabdor]

I am def seeing this was likely not your fault, albeit, a very unfortunate happening which is hard to find who or what is at fault.
but it kinda scares the crap out of me considering my own loading practices are as careful as your own and that this happened at all

Appreciate the comment. Blessed no one (my family or others was hurt).

I really appreciate all the dialog and feedback. I've learned a lot which I'll incorporate into my reloading practices although frankly I'm not itching to reload quite yet......

 

[Clabdor]

Good thing your both ok.
Is there a possibility of a carbon ring in the throat. How many rounds did you shoot before the situation happened.

The gun had a total of about 140 rounds fired through it. I cleaned the gun after the last set of rounds, so it would have had approximately 12 shots down the tube before it blew.

 

[Clabdor]

Take those other 2 rounds apart and reweigh the powder charge.

I will, but those are at an even higher charge weight. They aren't part of the 57.1 or 57.4. They would be 57.7. Regardless, I'll check them.

 

[Clabdor]

Well, I have read this entire thread because when something like this happens it is of concern to all of us. As others said, glad y'all weren't injured or worse. After reading everything the one thing that concerns me is that you loaded up new brass right out of the box without checking the OAL on it beforehand. Usually the chamber OAL exceeds cartridge specs a little so USUALLY a slightly long piece of brass doesn't make much difference. I know that you are using good quality components but things do happen. My procedure on all new rifles/barrels is to check chamber OAL with one of those little plugs from Brownell's in a neck shortened case and to measure the actual neck diameter with small hole gages or pin gages so you know the reality of your rifle. Then you need to check brass OAL and loaded neck diameter to know for sure that everything is as you want it to be. My take on this accident is that the chamber OAL is on the short side and the failed brass was just a little too long. At this point you can't check the chamber but you can check your brass to see if there is any length discrepancy worth worrying about and compare it to SAAMI. Hope this helps, really scary deal.

Good comments. Thanks. I used an Hornady OAL gauge on the chamber. I do that for all my rifles. I usually do 10 measurements just to make sure I have a consistent measurement with little chance of mismeasurement. I didn't measure the brass to be honest. I assumed (possibly incorrectly) that it would be trimmed to SAMMI spec. For all fired brass I clean, measure, trim, inspect, clean the primer pocket, camfer, relclean and then discard any brass which I think is sketchy. I don't need to eak out the last vestiges of brass life at this point in my life, so I usually chuck stuff if it is questionable.

 

[Clabdor]

You noted that the bolt was still in the locked down position. But the photo, that is not the case, or it might be the problem.

Is there any chance this rifle could be fired without the bolt fully closed?
Note in the photo, the lugs are not where they should be.
View attachment 1738268


The other odd thing is that it does not look like any gas escaped the relief hole.

View attachment 1738269

The case head is about what you get in a gas operated system when it’s over gassed. The extractor is what pulled the missing piece out. Did this happen when the barrel moved forward, or was the chamber not fully closed?

View attachment 1738276

Plenty of brass blown into the ejector andwelded to the chamber, so certainly a lot of pressure

Well....good question on the bolt closure, but I would guess no.....? Honestly don't know. As far as the vent holes - you are right. There is no gas escape residue, but not sure what that means.

 

[Clabdor]

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?

Nope - Felt good about the session and the rounds downrange. He had a good session on the rounds we loaded for him, and I was really just seeing if there was a better accuracy node a little up the ladder (which there wasn't....) For a couple of seconds, we didn't even really understand what had happened. My boy and I were both just stunned (not that we were hurt, just flummoxed).

 

[Clabdor]

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.

Good thought but no. Two different manf and his wouldn't fit in mine and vice versa. In addition, his looks completely different than mine.