Kaboom 💥 Today 😟

[Mike Matteson]

That was on the 12th firing. Did you ever check your case for separation in between firing? Or have you checked any of your other cases for separation at the base. I could detect the line on the interior of the base by the pictures you supplied which is showing case separation at the base. You didn't mention that you had check for case separation on any of those firing. It would be smart to check your cases from time to time for base separation. You don't need to check after each firing, but every few times. If you deteck separation, then you need to check all. After that every time.
I don't have any up dated reloading manual to see what the different is from one chamber to another. You were chamberinng to an AI case. I know that the 280AI case is longer to the shoulder than other AI cases. 280AI case are about .01" longer to the shoulder than other AI case. So you might check and see if the length is longer to the shoulder. That could be the problem is you are fire-forming case that the shoulder is moving forward a larger amount. Starting your case separation.
Sure lost with out my other manuals around. All I have is my No. 1 Nosler printed in 1976 reloading manual here with me.
I real feeling is the head spacing is off.

 

[Pdvdh]

Brittle brass.

 

[243winxb]

That was on the 12th firing

NO.

Op said - " 1x fired 708AI brass."

 

[Chadp82]

Wow. Glad you weren't hurt.

Just something for thought. Is it possible you had a short load? So it blew up like a pipe bomb? Too much space in a case can be a problem, it's not always too much powder. Maybe the dispenser got stuck and you only got say, half of the charge?

Depending on powder throw methods, could it be possible some previous powder was still present and maybe this was a first load of the reloading lot?

It is possible it is a brass failure, but if it were me I would think back to the reloading as well. I have a single stage press and with cases in the tray have skipped one or double charged one. I visually check how full each case is. Double charge is easy, the funnel won't let all of the powder out. Empty is empty.

I ask because with progressive presses and automated equipment available nowadays, maybe something was overlooked and or missed or not noticed.

 

[Roughrice]

That was on the 12th firing. Did you ever check your case for separation in between firing? Or have you checked any of your other cases for separation at the base. I could detect the line on the interior of the base by the pictures you supplied which is showing case separation at the base. You didn't mention that you had check for case separation on any of those firing. It would be smart to check your cases from time to time for base separation. You don't need to check after each firing, but every few times. If you deteck separation, then you need to check all. After that every time.
I don't have any up dated reloading manual to see what the different is from one chamber to another. You were chamberinng to an AI case. I know that the 280AI case is longer to the shoulder than other AI cases. 280AI case are about .01" longer to the shoulder than other AI case. So you might check and see if the length is longer to the shoulder. That could be the problem is you are fire-forming case that the shoulder is moving forward a larger amount. Starting your case separation.
Sure lost with out my other manuals around. All I have is my No. 1 Nosler printed in 1976 reloading manual here with me.
I real feeling is the head spacing is off.

I've had case head separation with 280AI with Nosler Sammi brass fired in Original Ackley Improved chamber just as you speak of.

I have never had the case rim destroyed that way though.
Now, I always use the paper clip tool to check when I see the ring develop on any case...especially after several firings.

 

[Mark37082]

You will more than likely never know what the real issue was. Defective brass seems to be the only plausible explanation knowing your level of experience. IX fired brass typically gets a visual review and standard measurements when loading. I would toss the lot or send to Lapua for inspection. Very scary situation.

 

[shinbone]

That break is just too smooth, uniform, and clean to be fracture line. Also the separation is at an odd spot for a typical case rupture - it is down at the very bottom of the case, where the case wall is thickest. I don't see any evidence that is a simple over-pressure situation. I gonna vote defective brass.

 

[DoneNOut]

Now that I've settled down with a night's rest I can add more info so I can help you help me.
(I might have identified a potential cause of the Kaboom. Stated at end)

Me condition: My right eye is a bit sore, I picked out some small fragments from the right side of my face, I'm really glad I didn't suffer worse. I wasn't wearing protective glasses. Never have my entire life. That changes now. I could have lost my eye.

Rifle condition: Has been cleaned, borescoped, and I only needed to replace the extractor on the bolt. The pieces of debris were not from the bolt thank God, but from the brass. Magazine is trashed.

Equipment:

Rifle action - American Rifle Company Nucleus

Barrel - New Benchmark 26" with chamber cut with a JGS 708AI reamer by Patriot Valley Arms, PA

Bullet - 162 ELDM seated to lands. 2.925

Powders:

708 fireforming - No pressure signs. (Primer pocket growth, case web fired size, primer inspections)

H100V - 44.5-46gr 2820s-2850s ragged hole groups .115 MOA
RL-17 - 44-45gr 2850s-2870s ragged hole groups .3 MOA

708AI loads. 5rnds ea. Some slightly flattened primers on all brass except kaboom round.

W760 - 47gr 2833fps ave with an SD of 6fps. MOA groups
H100V - 46.5 2808fps ave with SD of 18fps. Over MOA
RL-17 - 46gr 2865fps 2rnd ave with Kaboom on 3rd shot.

Primers: Fed 215M

Brass: New 308 WIN Lapua
Brass was sized to 708, then fireformed to 708AI. 200ct 708 rounds fired with no problems. Fantastic accuracy.

708AI rounds: The first 30rnds fired were shooting horribly. I discovered my neck to chamber clearance was practically zero and a bullet would not drop through a fired case neck. So, I turned the necks to allow a .007" clearance and removed the donut that formed in the case necks. (The sizing and fireforming thickened the case walls and gave a donut)

_______________________________________________________________________________________________________________________

NEW information:

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. Further evidence I now recall is the remaining rounds in the mag lost their bullets, and I had powder dumped all over my shooting mat. I don't know this 100% of course, and there is the evidence the case rupture is rather strange. However, I never intend to shoot with .0005 case neck tension. This is the only variable out of whack in all of this...

Counter Evidence to this theory:

There wouldn't have been enough room in the case for the bullet to get that deep. Potentially just 2.885 considering the powder column was near compressed. I shot the original 708 rounds at 2.880 with no problems.
Hmmm....

 

[FullCurl8]

Thanks for sharing this, when things like this happen it makes us handloaders double check our work, and maybe put our safety goggles on which I hate wearing. My experience is the Brass is always just a symptom on catastrophic failure, not the cause. It's just a soft metal vessel that requires near perfect support to do its job. I have seen this with a wrong cartridge used in a rifle before. This is not a case separating, that perfect line is just where it tore the case. And a bullet that pushed into a case would definitely mimic that for sure!
My suspicion is there may be bolt damage as well? OP did not say what action.

 

[DoneNOut]

The Brass is always just a symptom on catastrophic failures, not the cause. It's just a soft metal vessel that requires near perfect support to do its job. I have seen this with a wrong cartridge used in a rifle before. This is not a case separating, that perfect line is just where it tore the case.
My suspicion is there may be bolt damage as well. OP did not say what action.

See above for more info.

 

[lancetkenyon]

What case was used to fireform, 7mm-08 or 308 win? To much case stretch on the first firing can damage brass & cause case head separations, later.

For the case head to be gone, very high pressure may be the cause. When necking down brass, the loaded rounds neck diameter need to fit the chamber. If to large, the bullet gets crimped in tne case = Kaboom. Hard bolt closing would be a sign.

The clean cut is a little puzzling. To perfect. Two things come to mind.
The gap between bolt & barrel face may be excessibe. More then .010" What action are you shooting?
Some brass is manufacfured in 2 pieces, then formed. The case head is stamped & swaged to the case body, under very high pressure.

I can guess, but at times, we may never know the cause.
https://www.thehighroad.org/index.php?media/albums/kaboom.24/

Just make note...
AI chambers are cut about .004" short, to allow a crush fit on parent case brass. Every AI I have shot/owned gets hard bolt close on fire forming loads with virgin brass, regardless of if the bullet is jammed to the lands.

 

[VinceMule]

I would put a bore scope down the rest of that brass and check it out before using it. Do you still have ten fingers and thumbs?

Just make note...
AI chambers are cut about .004" short, to allow a crush fit on parent case brass. Every AI I have shot/owned gets hard bolt close on fire forming loads with virgin brass, regardless of if the bullet is jammed to the lands.

On the close-up of the brass, you see a very distinct line in the case which indicates case stretching and imminent case head separation/1


Someway, somehow, you had excessive headspace.

Lancekenyon mentioned a .004 number, on my own rifles I like .006-.008 which allows me to custom-fit the sizing where the bolt closing is snug. This additional "crush" eliminates any and all case stretching during fire forming. I found an up to a .006 variance in the length of head spacing on new Win and Rem brass, and I can not comment on Lapua. Fire forming with light pressure loads has always been problematic for the length of the headspace indicates a huge spread.

If the lack of clearance has created a pressure problem I can not comment on it. In the Mid 80's, it was popular in Registered Benchrest matches to shoot a zero clearance neck where there was only .0002 clearance at the most. I never had any problems with overpressure, and neither did my shooting friends. I did find later on that Bullet release on necks with .0002 created larger groups. So, if you had .0005 clearance you were ok, but ideal for accuracy.

I suspect that there is a mistake of some kind in your fire-forming process or headspace.

I neck turn at 30 caliber when I neck down and set headspace, I want a slight crush fit as part of the 30 caliber neck acts as a false shoulder. You NEED to feel some resistance on the bolt closing when fire forming, if you do not, you will for sure have case stretching, how much is unknown? I fire form with 14-14.6g of bullseye and a case full of cream of wheat, and I am sure there are better ways, but this method produces 95%+ formed cases.

 

[DoneNOut]

On the close-up of the brass, you see a very distinct line in the case which indicates case stretching and imminent case head separation/1


Someway, somehow, you had excessive headspace.

Lancekenyon mentioned a .004 number, on my own rifles I like .006-.008 which allows me to custom-fit the sizing where the bolt closing is snug. This additional "crush" eliminates any and all case stretching during fire forming. I found an up to a .006 variance in the length of head spacing on new Win and Rem brass, and I can not comment on Lapua. Fire forming with light pressure loads has always been problematic for the length of the headspace indicates a huge spread.

If the lack of clearance has created a pressure problem I can not comment on it. In the Mid 80's, it was popular in Registered Benchrest matches to shoot a zero clearance neck where there was only .0002 clearance at the most. I never had any problems with overpressure, and neither did my shooting friends. I did find later on that Bullet release on necks with .0002 created larger groups. So, if you had .0005 clearance you were ok, but ideal for accuracy.

I suspect that there is a mistake of some kind in your fire-forming process or headspace.

I neck turn at 30 caliber when I neck down and set headspace, I want a slight crush fit as part of the 30 caliber neck acts as a false shoulder. You NEED to feel some resistance on the bolt closing when fire forming, if you do not, you will for sure have case stretching, how much is unknown? I fire form with 14-14.6g of bullseye and a case full of cream of wheat, and I am sure there are better ways, but this method produces 95%+ formed cases.

So, I bumped the shoulders too far back on the 708 fireforming loads. I didn't have much bolt closure resistance I recall.

My bullet/case neck tension was .0005.
My case neck to chamber was .007

 

[243winxb]

AI chambers are cut about .004" short, to allow a crush fit on parent case brass.

I agree. But was the OPs chamber cut that way?