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

[tdbru]

I'm tending to agree with LRRPF52. the primer is not flattened nor cratered. extractor not blown off, bolt lugs all there. and the case head came off the bolt face pretty easy. also notice no case head material flowing into the ejector hole. Just one of those rare pieces of bad brass it appears. Of course the suggestions to get the headspace checked would be prudent as well. Even the lettering on the headstamp has not been squashed or obliterated. no black ring around the primer. I doubt the primer pocket has been enlarged. All the typical signs of an overpressure round are absent save the case head separation. However i've had case head separations on some of my reloads where i was going to get the very last load out of the case. Probably around load 25 or so. So there are case head separations without overpressure, but the brass usually tells you it's about to give up before it does by showing a bright ring around the case just above the web of the case. Another thought was that this case got caught in the annealing machine at the factory and was annealed all the way through, not just at the neck. However OP said 1x fired so that over annealed case hypothesis may not hold water. Anyway I too think it wasn't over pressure but just a bad piece of brass.
regards,
tdbru

[Warlock]

Is there a chance that the slug set back on the loading ramp?

I honestly have never had or witnessed a kaboom due to the slug being set back.

[lazyengineer]

I'm tending to agree with LRRPF52. the primer is not flattened nor cratered. extractor not blown off, bolt lugs all there. and the case head came off the bolt face pretty easy. also notice no case head material flowing into the ejector hole. Just one of those rare pieces of bad brass it appears. Of course the suggestions to get the headspace checked would be prudent as well. Even the lettering on the headstamp has not been squashed or obliterated. no black ring around the primer. I doubt the primer pocket has been enlarged. All the typical signs of an overpressure round are absent save the case head separation. However i've had case head separations on some of my reloads where i was going to get the very last load out of the case. Probably around load 25 or so. So there are case head separations without overpressure, but the brass usually tells you it's about to give up before it does by showing a bright ring around the case just above the web of the case. Another thought was that this case got caught in the annealing machine at the factory and was annealed all the way through, not just at the neck. However OP said 1x fired so that over annealed case hypothesis may not hold water. Anyway I too think it wasn't over pressure but just a bad piece of brass.
regards,
tdbru

Kind of, this one is odd. Because there does appear to be extrusion or deformation at the extractor area, and possibly at the ejector area. I thought so at second glance at least. but at 3rd glance, the primer isn't as flattened and the lettering isn't as flattened as typical with an overpressure. So some signs to me say overpressure, but some signs say... maybe not.

It is curious that it's a Lapua casing. That's generally viewed as the standard of high QC above all others, and I've not seen this sort of failure anywhere else yet.

[StoneHendge]

That's happened to me. I was running a 6 Grendel warm and the barrel's chamber didn't fully support the case walls. Meaning a much larger unsupported area than normal. I had Magnetto on and velocity was about 1k fps low. Your bullet was low because half your pressure bled out the mag well. I'd check your receiver's mag well - mine bowed out a little.

I'd also drop a bullet in the chamber and compare it to how it sits in your other Grendel. I'd also be wary of using the bolt and carrier again. I retired my bolt but did try to use the carrier again. It wouldn't cycle.

[Old Bob]

Back in the late 90's I had a kaboom in the middle of a 3 gun match shooting 5.56 NATO ammo re-manufactured by a local company. The carrier had significant damage. The bottom of it was blown off & there's a crack in it on the top, at the front. The bolt face & lugs look undamaged but I won't use it again. It still has a section of the rim stuck under the extractor along with the primer. The extractor is bowed & part of the extractor spring is sticking out from the back side of the extractor. While the magazine was blown out of my rifle, the mag well was undamaged. That lower is a billet lower & the mag well walls are pretty thick. It's stout as heck! I used that lower for another 15 years before replacing it.

[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.

This ones for you and everyone else helping me get on the right path.

Started doing some measuring today and this is what I found using my hornady COAL tool.

The COAL to the lands in my pistol with a hornady 120 Amax is 2.134...this is touching the lands!!!!

So it looks like COAL of 2.247 is way to long.

Put one of the rounds in question into a mag and dropped the bolt on it. Bolt completely closed but was difficult to open. Inspected the bullet and could see where the lands had engaged very deep on to the bullet. The bullet was not set back and came out with the case. Had the same OAL before and after.

For comparison I check 3 different bullets for OAL in my PSA pistol and in my rifle with a Lilja 319 barrel. What I found was also very interesting

Every COAL ran on average 130 thousands shorter in the PSA pistol compared to the Lilja 319.

Here are some more pics for ya'll to look over.

This is the bolt after cleaning it up.

[BowChamp]

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.
.

The case base came out of the bolt fairly easy.

The bullet hit the target about 20 inches low making a clean hole.

This complete upper came from PSA...they use Tool Cratf BCG'S.....although it isn't marked and I can't be forsure.

All the bullets were loaded...It was a new unopened box, 100 count.

See my latest post for your final question.

[BowChamp]

Textbook example of case head separation.

That normally points to a failure node in the brass.

You normally don’t see the extractor survive an overpressure event in the AR-15, and 1-2 bolt lugs often will shear off.

With the bolt and extractor still intact, I think you just had a bad piece of brass with stretching in that circumferential area around the case web.

Do you have any pictures of your once-fired brass that haven’t been re-sized?

Kind of what I was thinking at first...Bad case.

No I do not, I cleaned and loaded all my empties that day.

Please look at my latest report. Thanks

[BowChamp]

I don’t think PSA uses the compound chamber at their price point, so 2.247” even with a 120gr A-MAX shouldn’t jam the lands unless the chamber was cut really short.

OP will be able to tell if that COL is jammed by marking the projectile and chambering it, then extracting and looking to see if the rifling has made any marks on the ogive.

There have been a few parallel freebore chambers I’ve seen that would jam the lands because they were cut really short, but the norm is to have too much freebore in mass-produced barrels.

I did a comparison of COAL between my PSA pistol and my Lilja 319 barrel.

Check out the results.

Thanks

[Klem]

Bow,

I agree with the others that the pressure signs could have been a lot worse. That primer does look flat but there's no cratering into the firing pin hole, no pressure-pierced primer, no extrusion into the extractor groove, the lugs are still there and the base came out easily.

If I now run the touch-lands OAL of 2.143" in QL; assuming the bullet was set back as it slammed into the breech then the pressure climbs to 69.3K lbs (52K is the SAAMI limit). Add to that the pressure spike because it was jammed into the lands and that's a good reason for a case to come apart, but it is not as explosive as it could be.

I agree with the others, once a critical piece has had a an over-proof shock then it's time to replace it.

[StoneHendge]

If the bullet didn't set back all of the way and the bolt was somehow able to lock down and engage, there's your unsupported case above the web.

That's a pretty nasty looking crack between the lugs at about 4 o'clock in the 2nd picture.....

[BowChamp]

Bow,

I agree with the others that the pressure signs could have been a lot worse. That primer does look flat but there's no cratering into the firing pin hole, no pressure-pierced primer, no extrusion into the extractor groove, the lugs are still there and the base came out easily.

If I now run the touch-lands OAL of 2.143" in QL; assuming the bullet was set back as it slammed into the breech then the pressure climbs to 69.3K lbs (52K is the SAAMI limit). Add to that the pressure spike because it was jammed into the lands and that's a good reason for a case to come apart, but it is not as explosive as it could be.

I agree with the others, once a critical piece has had a an over-proof shock then it's time to replace it.

Yes Sir...a new BCG will be used for sure.

What are your thoughts on the Barrel/barrel extension??

[BowChamp]

If the bullet didn't set back all of the way and the bolt was somehow able to lock down and engage, there's your unsupported case above the web.

That's a pretty nasty looking crack between the lugs at about 4 o'clock in the 2nd picture.....

Didn't see that until I expanded the pic...that's why I posted it up. Sure looks like a crack to me. I'll be taking a closer look for sure.

Either way, I have another new BCG ready to go.

What are your thoughts on the Barrel/barrel extension???

[tdbru]

The barrel extension is what the bolt locking lugs lock into. if the bolt lugs were over stressed to the point of failure or cracking, how much damage was done to the barrel extension that the bolt lugs would push against. Worth inspecting or simply replacing. which might mean replacing the barrel. Or maybe better see if you can send the barrel along with the new bcg bolt to PSA and have them put a new extension on the barrel headspaced to the new bolt, if possible.

When i play around with seating depth chasing after that last fraction of MOA, or sometimes it makes a big difference, always check to make sure the loaded round chambers and extracts easily. so for a bolt gun i just take the striker out of the bolt and proceed to cycle all the hunting ammo i take hunting through the rifle to make sure every round chambers with no resistance and extracts with no bullets lodged in the barrel etc. For the AR i guess you just trust the safety.

i am a bit surprised that there is that much difference in the chamber throat dimensions between the two 6.5 Grendel rifles/pistols that you have. Something seems not right to me. give PSA a call and see what they say.

-tdbru

[A.D.D. AR]

BowChamp-
wow, that's a short chamber, indeed. I used to shoot 120 amaxes back in the day, but when 123 amax came out, I switched to them immediately- more forgiving ogive, and better BC.
If you still have a bunch of 120's, they can still shoot excellent, (maybe 15 thousandths off the lands) but with your short chamber you'll have to back down the powder charge for sure! maybe not worth it.
Glad you got it figured out & had no serious damage.

[Klem]

What are your thoughts on the Barrel/barrel extension??

Bow,

That is a difficult one. I am mindful that it is convenient for us to advise replacing anything that came into contact with pressure because we are not the one spending money to replace it. This is not a situation where the Government just replaces everything at taxpayer expense.

In your shoes I would replace the bolt and leave it at that. The barrel will take a stack of pressure and still be fine. The barrel extension took as much pressure as the bolt but we do not hear them failing as much as bolts. Fair to assume then the extension is stronger than the bolt and the bolt is therefore the canary in the coal mine. If the bolt is still pretty much still in one piece I would trust the extension and barrel is still fine. Otherwise you have a much bigger expense on your hands.

If that bolt doesn't have any visible cracks I would replace it but hang onto it for emergencies.

[lazyengineer]

I'm actually not that surprised. Grendel throats tend to run really short, for whatever reason. I haven't had it cause such a serious pressure spike, so much as prevent clambering and other annoyances.

[muvef]

Yes Sir...a new BCG will be used for sure.

What are your thoughts on the Barrel/barrel extension??

OP, I'm glad you're ok.

I would replace the barrel just for peace of mind. Is it ok? Probably, but I'd worry about a mishap if one of the kids were shooting it. Not worth it in my opinion.

Also, seems like it has a short throat, so in my mind it's a bad part. Scrap it.

My two Grendel's get significant pressure sign with AR Comp around 27.5 grn. Others use way more, but no way I could with my lot of powder.

Great advice above from the other replies.

[Happy2Shoot]

This ones for you and everyone else helping me get on the right path.

Started doing some measuring today and this is what I found using my hornady COAL tool.

The COAL to the lands in my pistol with a hornady 120 Amax is 2.134...this is touching the lands!!!!

So it looks like COAL of 2.247 is way to long.

The correct COAL for the 120 Amax is 2.245"

Email PSA and tell them what you measured. They cut it too short. End of story.

Tell them you want a replacement. Ship it all back and get a new one in return.

[BowChamp]

The correct COAL for the 120 Amax is 2.245"

Email PSA and tell them what you measured. They cut it too short. End of story.

Tell them you want a replacement. Ship it all back and get a new one in return.

Considering I had my head up my Butt and skipped one the most important steps in handloading, "COAL", I'm not concerned with any kind of warranty from PSA. :o

This one is on me!!!

I'm thinking the barrel is gonna get changed out too.