KABOOM!!! Come on in ....Seeking Advice/knowledge.

[BowChamp]

Factory upper came with BCG, 12' grendel, cabine gas. Fairly new upper, about 40 rounds fired through it.

Firing Handloads...Once fired Lapua Case, Rem 7 1/2, ARcomp 27.7 gr and Hornady 120gr Amax, COAL 2.247"

Fired a few rounds through one of my rifles then picked up the pistol and this is the result of the first shot fired through the pistol. Bullet hit the paper, 20" low, at 100yds.

Gun has no visible damage.

Damaged the magazine and two rounds inside it.

Charge handle required a very light tap with the palm of hand to open and front part of case was very easy to remove from chamber.

No one was injured!!!

See pics below and Discuss.

[Dt219]

Holy hell

[Happy2Shoot]

Fixed firing pin? Out of battery?

I assume this is a PSA upper?

Where did you find this load data? Only published load I can find is for 120gr Gold Dot at 25.3gr. You were at 27.7gr!


Alternative guess:

Over charged by 2.5 grains of powder. Port pressure way over gassed, due to pistol length gas system and over charged ammo. Super rough PSA chamber (I know I have one and had to fix it with a chamber hone) didn't let go of the case in time and the extractor ripped the rim off.

[HKGuns]

If you weren't over charged, you were on the high end based on powder burn rates and similar charges I could find data on..........I too couldn't find any load data for that particular combo.

Every rifle is different, which is why the long standing advice is to work your loads up, monitoring for signs of pressure. I'll assume you did that before shooting.

I think extraction, otherwise I think you'd see bolt lugs sheared and / or other more significant damage.

Regardless, you got lucky, learn from it.

[lazyengineer]

Oh Wow! Glad you are OK.

FWIW, I run 27.8 gr ARComp under 120 SMK. And they run fine in my 20". I will say though, you have to be careful with Grendel with OAL. Many loads that are magazine length, are still too long and will engage in the lands. Which isn't good, as that can cause a pressure spike and accuracy issues, so not sure if you tested that. But I have to run my OAL closer to 2.22", or something like that, to clear, in my own chamber. I also don't use Lapua brass. That brass likely has a smaller capacity, which will mean a bigger P spike. Those two factors combined could result in a spike, but to be honest, I still wouldn't expect a complete Kaboom like that. The head is completely sheared off.

Cause is not obvious right now. Could be a combination of partial barrel obstruction being a brand new barrel, P spike from wedging into the lands, P spike from case-volume, and P-spike from that round being on the higher end of the tolerances of your load practices. From your description, it sounds like the pressure released definately happened within the first few inches at peak (well, by definition, at peak), and so the bullet didn't have full energy of acceleration for the dozen inches, and so it impacted very low.

So I guess some basic questions:
Show us what the head and case bodies of the other rounds look like
Show us what the remaining loaded rounds look like
Pull apart 5 rounds and carefully measure the powder weight, and examine for any inconsistency or contamination. Does the powder look like AR Comp?
Go ahead and examine the bullets - are they all really 120's, or did a heavy slip in there? (not likely, but they're out in your hands anyway)
Test your seating depth in that chamber (Hornady tool, or just make a bullet with a sharpe and see if it gets scratches on the ink by engaging the lands)
Was the barrel cleaned prior to firing?
Was the new barrel inspected prior to firing - even if cleaned, to assure a patch or other residue wasn't in there?
Was this a slam-fire, or did you pull the trigger?
Check your remaining loaded roads in that upper = does the upper readily close and rotated on them? Do they readily come out, when you cycle the charging handle?
Tell me about your brass processing - could there have been left over debris of some sort in them? (thus reducing case capacity) I've had that happen once, but usually obvious when the powder all comes spilling out and won't fit.


PSA customer service is actually quite good, so it's possible they will take it back for inspection or replacement, though it sounds like nothing was damaged. I find it interesting the casing ruptured and failed, before the bolt lugs did. I don't know what to make of that. If it were an OOB, that would mean the 1/4" or so of clearance betten an open bolt and rotated bolt was somehow bridged by something longer than your firing pin. That would be remarkable, and I have my doubts. But who knows, being brand new, was there debris that got launched into the firing pin upon the snap on the firing pin?

Don't know - often these are obvious, and I'm keen to learn what caused this one. (FWIW, in most Kabooms today, the first qustion is "do you own a .300 blackout", and much of the time, that's where it is - but obviously not the case here!)

[lazyengineer]

Also, the interior of that case head looks... odd to me. I haven't sectioned a Grendel, and it's failure mode form may not be how it started. But I was under the impression there was typically more rounded slope at the base, where the walls merge into the case-head on the inside. This one looks a bit thin there. Normally headspace related failures occure in the middle of the case body, and there's enough base to still seal. And .223 cases are designed for that, with a bit thicker bottom 1/3 of the case or so. That Lapua Grendel case... I donno. Lapua internal case dimension nuances combined with excessive headspace from the factory, is not something I'm prepared to say was the cause - but worth a moment to confirm that the headspace is correct, if you have ability to do so.

[lazyengineer]

Ah wait - I do see it now. The head shows extrusion into the ejector and extractor areas. That's definately not headspace nor OOB, as both of those would relieve the pressure before enough pressure builds to flow the brass like that. THat's a massive overpressure, not a case failure. So now we're looking at overcharge or obstruction of some sort, or combination of those items. Definatelly please confirm what your cleaning and inspection practices were with the new barrel.

Also, double bonus points on the bolt holding up to that. That went just a wee bit over the 52,000 PSI rating.

[A.D.D. AR]

Bow Champ- glad you are OK!!
my guess - a 120 grain Amax at 2.247'' is jammed into the lands. it has a way different ogive than the 123 amax (or now eldm)
-in SAAMI chambers a 120 amax usually ends up about 2.190'' or so.

[BowChamp]

Alright, Ya'll bear with me, I'm watching the Grandsons today ...... So might not be able to answer all the questions at once.

Here Goes!!

[BowChamp]

Fixed firing pin? Out of battery?

I assume this is a PSA upper?

Where did you find this load data? Only published load I can find is for 120gr Gold Dot at 25.3gr. You were at 27.7gr!


Alternative guess:

Over charged by 2.5 grains of powder. Port pressure way over gassed, due to pistol length gas system and over charged ammo. Super rough PSA chamber (I know I have one and had to fix it with a chamber hone) didn't let go of the case in time and the extractor ripped the rim off.

Floating firing pin

Not out of battery...bolt was completely closed and locked

Yes....PSA Complete Upper.

[Happy2Shoot]

Floating firing pin

Not out of battery...bolt was completely closed and locked

Yes....PSA Complete Upper.

WOW! Bolt was still closed?!

Is it the wrong chamber? Extra long head spaced?

I guess it could just be bad brass.

[BowChamp]

Oh Wow! Glad you are OK.

FWIW, I run 27.8 gr ARComp under 120 SMK. And they run fine in my 20". I will say though, you have to be careful with Grendel with OAL. Many loads that are magazine length, are still too long and will engage in the lands. Which isn't good, as that can cause a pressure spike and accuracy issues, so not sure if you tested that. But I have to run my OAL closer to 2.22", or something like that, to clear, in my own chamber. I also don't use Lapua brass. That brass likely has a smaller capacity, which will mean a bigger P spike. Those two factors combined could result in a spike, but to be honest, I still wouldn't expect a complete Kaboom like that. The head is completely sheared off.

Cause is not obvious right now. Could be a combination of partial barrel obstruction being a brand new barrel, P spike from wedging into the lands, P spike from case-volume, and P-spike from that round being on the higher end of the tolerances of your load practices. From your description, it sounds like the pressure released definately happened within the first few inches at peak (well, by definition, at peak), and so the bullet didn't have full energy of acceleration for the dozen inches, and so it impacted very low.

So I guess some basic questions:
Show us what the head and case bodies of the other rounds look like
Show us what the remaining loaded rounds look like
Pull apart 5 rounds and carefully measure the powder weight, and examine for any inconsistency or contamination. Does the powder look like AR Comp?
Go ahead and examine the bullets - are they all really 120's, or did a heavy slip in there? (not likely, but they're out in your hands anyway)
Test your seating depth in that chamber (Hornady tool, or just make a bullet with a sharpe and see if it gets scratches on the ink by engaging the lands)
Was the barrel cleaned prior to firing?
Was the new barrel inspected prior to firing - even if cleaned, to assure a patch or other residue wasn't in there?
Was this a slam-fire, or did you pull the trigger?
Check your remaining loaded roads in that upper = does the upper readily close and rotated on them? Do they readily come out, when you cycle the charging handle?
Tell me about your brass processing - could there have been left over debris of some sort in them? (thus reducing case capacity) I've had that happen once, but usually obvious when the powder all comes spilling out and won't fit.


PSA customer service is actually quite good, so it's possible they will take it back for inspection or replacement, though it sounds like nothing was damaged. I find it interesting the casing ruptured and failed, before the bolt lugs did. I don't know what to make of that. If it were an OOB, that would mean the 1/4" or so of clearance betten an open bolt and rotated bolt was somehow bridged by something longer than your firing pin. That would be remarkable, and I have my doubts. But who knows, being brand new, was there debris that got launched into the firing pin upon the snap on the firing pin?

Don't know - often these are obvious, and I'm keen to learn what caused this one. (FWIW, in most Kabooms today, the first qustion is "do you own a .300 blackout", and much of the time, that's where it is - but obviously not the case here!)

I have no other cases fired from this pistol...was the first and only round fired from this pistol that day. ( did fire about 30 of them in one of my rifles and all is well)

The rest of the loaded rounds are at the farm. I'll work on pics of them.

All charges are weighed on at a time and the number of dropped loads are recorded, Arcomp was the only powder in the loading room. All equipment is cleaned then powder is brought in.

Cut open a new 100 count box of Hornady 120gr Amax's.

I'll will definitely check the seating depth of the chamber with the 120gr amax using my hornady tool. (Will get back with this one when I get a chance)

Yes, barrel was cleaned the night before and I always look through them when done. (Bullet did hit the target at 100yds)

Was locked on target and squeezed the trigger...shooting for groups...was the best group I've ever shot.. but is was just one shot!!! LOL!!!

I will be checking for fit and finish. ( Will let you know) The round fired was loaded from the magazine by dropping the bolt and closed with no problems.

Brass is tumbled, wiped with a rag to remove any media dust, full length sized, tumbled again to remove case lube, wipe with rag to remove media dust, necks and primer pockets are cleaned, primed with hand primer, charges individually weighed then bullets are seated...(COAL is checked on every one as they are seated)

That about sums it up.

Not concerned with warranty at all. Just want to figure out what I did wrong (May be the hard way.... but I always learn from my mistakes)

Almost forgot...I do not own a 300 blackout!!! LOL!!!

[BowChamp]

Also, the interior of that case head looks... odd to me. I haven't sectioned a Grendel, and it's failure mode form may not be how it started. But I was under the impression there was typically more rounded slope at the base, where the walls merge into the case-head on the inside. This one looks a bit thin there. Normally headspace related failures occure in the middle of the case body, and there's enough base to still seal. And .223 cases are designed for that, with a bit thicker bottom 1/3 of the case or so. That Lapua Grendel case... I donno. Lapua internal case dimension nuances combined with excessive headspace from the factory, is not something I'm prepared to say was the cause - but worth a moment to confirm that the headspace is correct, if you have ability to do so.

Cases were once fired by me.

No barrel obstruction.

The front part of the case came out of the chamber very very easy.

The head of the case was lightly stuck in the bolt as shown in the pics. That is exactly how it was when I removed the BCG... about a minute after the smoke cleared.

I have Go/No Go gauges on the way.

Again, the bolt was not very hard to open by hand. Just bumped the charge handle with the palm of my hand was all it took.

I'm wondering if i had the bullet jammed into the lands?? We shall see.

I'm wondering if I jammed the bullet into the lands.. We shall see.

[BowChamp]

Bow Champ- glad you are OK!!
my guess - a 120 grain Amax at 2.247'' is jammed into the lands. it has a way different ogive than the 123 amax (or now eldm)
-in SAAMI chambers a 120 amax usually ends up about 2.190'' or so.

I find this very interesting!!!

As stated, I'll be checking this.

[Klem]

BC,

The important thing is you are OK. It's not pleasant to have that happen.

I have seen this in Blackout in a Remington bolt gun. The guy was shooting about three benches from me and loading at the range. He loaded a heavy bullet (subsonic) on top of a charge meant for a light bullet (supersonic). So a 220gn bullet when the charge was meant for a 110 or 115 bullet. A bigger than normal boom. Smoke all around him and people looking at him. The bolt was sticky and the base of the case split away and looked exactly like yours. It was hammered into the bolt face so tight he never got it out. Maybe he could have been more gentle but I saw big gouge marks in the bolt face where he had used tools and an order for a new bolt.

Yours looks similar but less pressure perhaps if that case base was not welded into the bolt face and came out of the bolt face without too much fuss.

That appears to be an overpressure incident at the time of firing. The only place overpressure can go when the bolt is in battery is the thin unsupported void between the front of the bolt lugs and the start of the chamber. Obviously it could simply overwhelm the bolt lugs but they held firm at whatever pressure the case split.

Using the volume of a Lapua case after sizing (35.92gns water) in Quickload your load predicts 58.7K psi and 105.5% compressed. It is over SAAMI but I would not expect such a catastrophic event. Plus, if you have fired the same load previously and it was verging on case splitting then there would have been other indicators; sticky unlocking, flat primers, unusual recoil in the earlier rounds. That sheared case is equivalent to a deliberate overproof test to destruction by a manufacturer.

If you poured powder up to the case mouth and compressed a bullet into it then maybe, but you would have seen and felt this when reloading.

I do not have data for the 120AMax but I do for the 123AMax and the bullet's OAL to touch lands is no different than most others. What I mean is, the spike pressure that happens when a bullet is jammed in the rifling is unlikely to be the case here. Do you have an idea of the throat in that rifle? The headspace might be fine but the throat is tight. Or the case OAL is too long for the chamber's neck and it crimps into the bullet when it goes into battery.

My money is on a bullet that could not move at the time. Neck of the case crimped into the bullet, or a throat/barrel obstruction. Maybe the diameter of the bullet was too wide for the bore (manufacturer error).

How easy was it to get the case base out of the bolt?

Where was the offending bullet hole on the target, and was it a nice round hole (stable bullet)?

What is the brand of bolt - very impressive that no lugs broke? I wonder if the bolt is now weakened.

You could measure the diameter of all the rest of the bullets in that box.

Also, I would check the OAL to know exactly when those bullets touch lands.

If a heavier bullet was loaded into the case accidentally you would know this already - whether you even have them and how close are they to the 120box on the shelf etc.

Again, all good that you're OK but you do need to know what happened to restore faith in the gun and ammo or it will happen again.
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