Kaboom 💥 Today 😟

[Pdvdh]

I had a conversation with someone who fireforms a lot a brass into AI. He pointed out to me that AI fireformed brass is being stretched .080 to .100" upon fireforming and the cases don't kaboom ever. That is by orders of magnitude more than I could ever possible cause a kaboom from .003".

,002 bump has become the standard.
.004 bump is what Alex Wheeler likes

AI fire-formed brass with the case head held in contact with the bolt face (as in crush fit upon bolt closure) is blown forward in the shoulder area, where the case brass has been annealed, is thin, and malleable. Your ~0.003" gap between case shoulder and chamber shoulder is insignificant. Not a cause for this separation at the extractor groove.

On the other hand, I think no casing at the extractor groove, or in the location ~0.200" forward from the case head (where case heads typically separate) can be "stretched" 0.080" to 0.100" without separation failure. The case web brass isn't annealed, and isn't very malleable. It can stretch smaller amounts prior to separation. Not 0.080" - 0.100".

Good cases in properly chambered bolt actions only blow out where your's did under excessively high pressure.

BUT... that casing certainly could have been manufactured with a defect which compromised it's pressure containing strength. Causing it to rupture at normal cartridge pressures.

As someone else already suggested... I'd throw away the rest of that Lot of suspect Lapua casings. I'd also contact Lapua. Share your incident and pictures. Send them the ruptured casing, if they expressed the interest in running some laboratory tests. Since you didn't suffer any permanent debilitating injuries.

 

[MagnumManiac]

Wouldn't the tendency to "fuse", torch, cut, and melt steel/brass around the bolt face depend on both the pressure level and the rate at which the pressure is released? This casing web separation largely removed the case head from the body. Pressure released rapidly might not torch and weld the bolt face and surrounding metal. Even if excessive pressure caused the rupture. We know pressure was released quickly, as measured bullet velocity was 2,100. 600fps slower than sister loads that didn't rupture.

Yes, this single casing could have been defective. The location of separation at the extractor groove rather than nearer the 0.200" datam suggests defective brass. On the other hand, it did survive a 1st firing without the fireworks.

If you've ever seen a similar case head separation in your gunsmithing career, feel free to say so. I haven't.

You've tagged angry emoji's in response to my posts. Yet... close your posts with "Cheers".

So... generally a cheery guy? Who disagrees angrily?

I honestly believe you don't know what you're talking about. An excessive pressure event, not a case failure, ALWAYS results in case FLOW into every possible recess in the bolt face, and obviously when the case ruptured due to a case defect, the gas was correctly directed into the mag well. Like it's supposed to…
My question to you is…how many ruptured firearms have you seen and how many have you determined the cause of such ruptures?
I have seen dozens in myriad of scenarios, such only 1 being caused by a case rupture very similar to this. Excessive pressure, nor excessive headspace caused any of this.

 

[243winxb]

Possible cause of all this. I discovered my neck tension was .0005 interference fit. Practically nothing! I thought I had .0015 min. I think it's possible the kaboom round had the bullet pushed back into the case upon chambering and created the problem. This is the only error I can isolate on my behalf. My gut is telling me this was the cause.

the low neck tension allowed the bullet to move out of the case to soon. This may cause a 2nd pressure spike. It acts like a plugged barrel.

" RL-17 - 46gr 2865fps 2rnd ave with Kaboom on 3rd shot." Double based powder containing nitroglycerin can do strange things.

46 grs woulld be Hornadys maximum for a standard 708.

The action companies claim of " Remington 700 Footprint " not even close. Where are the "3 rings of Steel? " Controled feed, not in Remington.

 

[DoneNOut]

" RL-17 - 46gr 2865fps 2rnd ave with Kaboom on 3rd shot." Double based powder containing nitroglycerin can do strange things.

I didn't have any problems with the first 7lbs of my RL17 jug. In fact I haven't ever had a problem with double base powders in 25yrs.

46 grs woulld be Hornadys maximum for a standard 708.

I was able to load up to 45gr with my particular lot of RL17 when shooting 708 in the gun. I added one more grain of powder when shooting 708AI in the gun. As is common for loading an AI.

The action companies claim of " Remington 700 Footprint " not even close. Where are the "3 rings of Steel? " Controled feed, not in Remington.

The Remington 700 Footprint claim by various companies making actions just denotes the action screws will line up with a stock made for a Rem 700. A means to standardize. ARC, Zermatt, Aero Precision, to name a few all have Remington 700 footprint standard. Beyond that there isn't anything claimed about the action features being Rem 700 in design.

 

[pavementends]

Gingerman, Glad you are intact with all fingers and both eyes. I personally have never seen a failure like you posted. A great many opinions expressed some of which might have read your original post. Again glad you are not injured.

 

[Seabeeken]

I see you used W-760. When I was working up loads for my 243AI with 760, I found crazy pressure spikes with mid level loads. These loads were all charged the same and I would get a normal pressure case and then an extractor mark and flat primer from the same charge weight. I've never used 760 since. Was this by chance a load of 760? If you're sure it was a bad case, I would send them to Lapua for testing and comment. I suspect a wild pressure spike, especially if you were working near the upper end of load data

 

[DoneNOut]

I spoke to a Lapua rep today. He had 40yrs experience shooting AI cartridges and had a couple of his own kabooms to learn from along the way. We identified the likely cause. I'm ready to proceed clean slate again.

Edited: Bob ran my load through Quickload and determined the 46gr RL17 was within norm parameters for 708AI.

 

[Straight Shooter]

When I first started reloading I used to get that with a lot of my 308 brass. I was using LC sniper bras from 1966. Had it happen on multiple occasions and I just figured it was worn out brass until I learned I was setting the shoulder back too far and stretching the brass too much. Yours is different because it was only on your second sizing.

 

[Doom2]

I spoke to a Lapua rep today. He had 40yrs experience shooting AI cartridges and had a couple of his own kabooms to learn from along the way. We identified the likely cause. I'm ready to proceed clean slate again.

And the likely cause?

 

[DoneNOut]

And the likely cause?

The 708 brass needed to be tight against the chamber and have resistance closing the bolt. I didn't have that resistance. When I sized the 308 into 708 I sized them down too far.

The bent paperclip trick won't detect where this case head separated. So, I am trashing the brass and starting over.

 

[shinbone]

Lapua should notified - there may be other cases out there with the same defect.

 

[DoneNOut]

Lapua should notified - there may be other cases out there with the same defect.

Well, its been ruled as my fault. I am not disbelieving the notion, but I am surprised that a few thou stretching on 1X fired case causes the rupture.

 

[Bob Wright]

It's such an amazingly clean break and evidence of a fracture remaining. I'm thinking bad brass too. Something might have happened during the initial drawing operation. Maybe a punch tooling change folded a void into it?
I'd be cutting some up just for education. The rest is scrap.
I'd volunteer my mill if you want to send a few.
Here is tutorial on Peterson's process.

Drawing Brass | How Cartridge Cases Are Made | Peterson Cartridge

See the brass rifle casing manufacturing process at Peterson Cartridge from raw brass coils to the finished casings we deliver to you.

www.petersoncartridge.com

 

[shinbone]

Like I posted earlier, and JMHO, but that is not a fracture surface showing at the failure sight. I've done some failure analysis in previous jobs, and no way does metal that fails by being strained beyond its ultimate strength leave such a smooth and uniform surface morphology. There are two different types of geometry seen here which argue against a simple overpressure of an intact case. First, overall, where the fracture meets the case circumference is perfectly uniform and straight all the way around the case. Second, on the microscopic scale, the surface of the failure is very smooth and has a perfectly uniform curve in two dimensions for its entire visible surface - there are no chevrons, dimples, or other hallmarks of a rupture in the metal. The evidence says it is a defect in manufacturing. Again, JMHO.