I had a partial case head separation using a 1.8oz buffer

[StoneHendge]

Feed cone is completely separate operation from reaming the chamber.

Found a relevant thread on Sniper's Hide titled "Grendel-like Belted Magnum Problem" HERE.

Thanks. My takeaway is that that would lead to the chance of individual operator error in the manufacturing process.

I always wondered how it was even possible with my exploding McGowan 6mm Grendel. But the muzzle threads were a hack job (which ruined the threads on the comp I installed) and the gas port wasn't drilled deep enough. I always theorized that the gas port was drilled for 6.5 Grendel. Given what I recall the chamber looking like with a case in it versus my BHW 243 LBC, it almost makes me think a bit (or whatever they use) for 6.5mm was used instead of 6mm.

[Fess]

Lapua's design, being earlier in grendel's product life, could it be its web/corner was not "exposed" (not unsupported) by the bolt face depths being 0.125 back then? I wonder, I was not into grendel at that time.[/FONT][/COLOR]

The Alexander Arms Grendels all had the deeper bolt IIRC. The deeper bolt was to compensate for the thicker rim of the parent brass vs 223. As I recall, the Grendel used the same bolt that was already in production for the 50 Beowulf. The Beowulf had been in production a couple of years before the Grendel was released.

Part of the confusion about bolt depth came from what we now call supply-chain issues. People wanted Grendels but the correct bolts were not available. This led to use of the existing .125 bolts that had been used in 7.62x39 AR15's. Interestingly, since those .125 AR15 bolts were a known problem area for Colt's earlier 7.62x39 AR15, when Colt was later given a contract to make more 7.62x39 rifles for Yemen, they changed the the design and used a variant of the beefier AR10 bolt in the CK901.

[BluntForceTrauma]

Note, for this comment, post #61, it's a pic of the Odin barrel chamber chamfer, a 2-step angle radiusing... [FONT=&amp]It looks like Odin does a double angle chamfer and the step appears to line up with the steeper/deeper chamfer.[/FONT]

GF, what you're calling a "double-angle chamfer" is really just the standard M16/5.56 way of doing it. First they do a 120° cone to help bank an errant bullet tip into the chamber, and then they radius the edges of that cone .0625 where it meets the chamber mouth to round off the edge.

Googled "Sectioned 5.56 Case" and found the attached. Looks like the "web" thickness mates up just fine with the M16 standard feed cone dimensions.

Note also how the difference in web thickness allows the FC case to hold more powder than, for example, the PMC case.

[DeNinny]

GF, what you're calling a "double-angle chamfer" is really just the standard M16/5.56 way of doing it. First they do a 120° cone to help bank an errant bullet tip into the chamber, and then they radius the edges of that cone .0625 where it meets the chamber mouth to round off the edge.

Googled "Sectioned 5.56 Case" and found the attached. Looks like the "web" thickness mates up just fine with the M16 standard feed cone dimensions.

Note also how the difference in web thickness allows the FC case to hold more powder than, for example, the PMC case.

It's interesting that Bill Alexander's quote posted earlier is basically stating that the feed cone should not follow the standard M16 configuration. And it's because of the unsupported wall issue.

To me, the issue is that the literal wider diameter of the grendel case relative to the 223/556 case is structurally weaker (all other things equal) than the higher curvature 223/556 case with smaller diameter. It's similar to how an archway door is structurally stronger than a rectangular door. This could also be why the belt phenomena tends to happen more in the grendel.

Also with more total powder in a grendel round, I'm pretty sure this will put more point force on the brass relative to a 223/556 one.

[BluntForceTrauma]

I think Bill Alexander was thinking that if one wants to maximize the powder capacity of the 6.5 Grendel case, the best way — he called it an "old artillery man's trick" — is to reduce the web thickness. But, then, the engineering logically followed that the feed cone of the chamber design must be altered to compensate for this.

Everything is fine when properly engineered; when the chamber is dimensioned to mate with the case. Companies that don't bother with the details, well, they experience issues. This is analogous to the details required for dedicated Grendel bolts and extractors and magazines.

[grayfox]

GF, what you're calling a "double-angle chamfer" is really just the standard M16/5.56 way of doing it. First they do a 120° cone to help bank an errant bullet tip into the chamber, and then they radius the edges of that cone .0625 where it meets the chamber mouth to round off the edge.

Googled "Sectioned 5.56 Case" and found the attached. Looks like the "web" thickness mates up just fine with the M16 standard feed cone dimensions.

Note also how the difference in web thickness allows the FC case to hold more powder than, for example, the PMC case.

Good piece of info. Thanks. But in the Grendel's case with certain types of brass, looks like that original 556 design can run into problems. Btw my monster 6Arc barrels have the single angle chamfer cut - they seem to be doing great. And my BA barrels, and Uintah. 'Course I don't have any Lapua brass to complete the apparent problem-child "combo".

[LRRPF52]

Yes - the extractor was in good shape, but the bolt was out of spec after this firing per seating the no-go gauge.

The more I have thought about this since yesterday, the more I am wondering about the bolt face depth.

If you had an out-of-spec bolt face depth that exceeds .136”, and a properly-cut chamber, it could also cause this to happen.

The fact that your extractor is intact, there aren’t any ejector extrusion marks or extractor pocket ledge shearing, and primer has a nice dimple on it all point to a well-within normal chamber pressure.

The flat primer is often seen in excessive headspace, when the primer backs out and slams against the bolt face, followed by the case re-seating over it due to brass expansion.

I need to go look at your headspace measurements again.

"Note: all these (2.246 - 2.26) may be too long for throat length. In the 123 Hornady BTHP, I had bullets possibly stick in the lands and had click-no-bang, and then trouble extracting the unfired cartridge"

At the time, I theorized that it was a jam into lands issue, but this didn't exactly line up after I got the Hornady COL gauge which found jam length of 2.3050 for the HPBT and 2.310 for the ELD-M.

It is interesting that I've only noticed the ring on one other case out of the 40+ I've shot in that batch so far. Next step is actually measure the powder from a few rounds when I get my puller...

Click-no-bang is a telltale sign of excess headspace.

Firing pin hits the primer, which just pushes the floating cartridge forward in the chamber without activating the primer.

[LRRPF52]

I understand safety at the field level, and the engineer is responsible for the system safety he develops or endorses.
I see trend specific to one component, and compelling explanation, combined with a large body of near-miss warning signs .

When you see a failure mode trend, and then see a difference that readily explains that failure mode - you call it out.

What I am also seeing, is what I see at the field level safety - of experts who have always said it is one thing, are the slowest to see the obvious when pointed out, and counter to their own bias.

Go look at those 4 photos, look at the fact that 3 kabooms in the last year - only with that brass, amd look at the warning tell of the ring shoulders. I'd fire an engineer who didn't call this out. It might also only fail in certain barrel at certain gas settings. Are you OK with that? I'm not.

From the engineering side, there are basic principles of pressure, axial stress, torsion, loads, factors of safety, metallurgy, etc.

These are all essential to know and be familiar with in firearms engineering, but you really need more specific experience in firearms engineering to understand what is going on.

I’ve seen several people in this industry now, including guys I highly respect who have done extremely well for themselves financially, who made some of the most egregious and erroneous statements about the basics of firearms engineering.

One of them, who went on to start and grow a very popular company, told me to my face that he thinks, “Bolt thrust is bullish*t.”

Bolt thrust is a fundamental reality of basic locking breach repeating firearms, where axial stress is placed on the bolt from the contained pressure in the system.

Same with bolt lug torsion on a rotating bolt design when the gas system is not timed correctly.

Metallic cartridge case metallurgy is also a fundamental discipline, where various manufacturers weigh the engineering and financial trade-offs as to how they will formulate their brass alloys.

Lapua chooses to focus on the best possible metallurgy, combined with tight tolerances on case dimensions internally and externally, with emphasis on measured aspects of flash hole performance relative to primer spark penetration depth into the propellant column.

The cheaper, softer brass manufacturers focus on volume production, so they make design trade-offs relative to areas of the case to keep them within FoS based on the SAAMI MAP, MPSM, and MPLM.

Cartridge manufacturers have to batch-test multiple samples within lots, which are then fired through instrumented and calibrated test breeches.

Reputable component manufacturers do their own testing, the more strenuous, the better their reputations tend to be.

Lapua has been the gold standard in that space for many decades.

A lot of people might read this and constrain my comments to their own situation, where they own and shoot only 1-2 of these firearms in this cartridge.

In reality, I have lost track of how many 6.5 Grendels I have tested over the years, while owning many, ranging from the longer barrels on down to the 12” guns.

I have had nothing but boringly-repeatable results with the Lapua brass. Then again, I’m very discerning about what barrels and chambers I use.

I have given some companies the benefit of the doubt by taking a chance with their barrels, bolts, and chambers.

Some worked out, and others didn’t.

I think this incident is starting to look more and more like a serious excess headspace problem, nothing to do with the brass.

[DeNinny]

I'm still seeing a combination of issues and it's still not clear which ones are the most likely. Excessive headspace is on the table for sure, but I need to understand by exactly how much? Is it 0.1", 0.01", or 0.001"? Because when I look at that distance as compared to the size of the feed cone depth, I don't see it mattering as much.

To me, the brass, feed cone depth, and headspace are all still on the table. I can't rule any one out.

[grayfox]

Still reading, and still learning.
Stepping back for a minute however, and agree there might be some uncertainty as to what exactly happened or combined to happen, one takeaway for sure is, if you change anything, gun, brass, load, bullet, whatever, must back down and start up again as to load weights. Too many things can happen or combine to happen, to make charging right in, so to speak, OK.

[LRRPF52]

When I have talked about bolt face depth with Bill in the past, he was pretty clear that it’s .136” +0.000/-.003” allowable. So a .133” bolt face depth would be allowable, but not a .138”.

If you tolerance-stack a deeper bolt face with a deeper-than-allowable feeding cone, and that case is able to expand that far back, that’s a recipe for making the brass find the path of least resistance.

This brass looks like it did exactly that. One thing I think everyone can agree on is that the brass was not supported in the location where it failed. Had that section of the brass been contained within the chamber walls, it would have just obturated against the wall, then de-obturated a bit when the pressure subsided.

Combined with the fact that he had Failure To Fire/Activate primer malfunctions before with another load (bang-click), and the bolt able to close on a NO-GO gauge, with the extractor still intact, I think we’ve narrowed it down pretty well to dangerously-excess headspace.

[DeNinny]

When I have talked about bolt face depth with Bill in the past, he was pretty clear that it’s .136” +0.000/-.003” allowable. So a .133” bolt face depth would be allowable, but not a .138”.

If you tolerance-stack a deeper bolt face with a deeper-than-allowable feeding cone, and that case is able to expand that far back, that’s a recipe for making the brass find the path of least resistance.

This brass looks like it did exactly that. One thing I think everyone can agree on is that the brass was not supported in the location where it failed. Had that section of the brass been contained within the chamber walls, it would have just obturated against the wall, then de-obturated a bit when the pressure subsided.

Combined with the fact that he had Failure To Fire/Activate primer malfunctions before with another load (bang-click), and the bolt able to close on a NO-GO gauge, with the extractor still intact, I think we’ve narrowed it down pretty well to dangerously-excess headspace.

Thank you for that dimension. Just using your numbers, I get .138" - .133" = 0.005" difference. And so if I understand your position correctly, you are saying that, in this scenario, the OPs casing was roughly 0.005" more unsupported, and possibly more if you add headspace. And this distance is what is considered dangerously excessive?

To me, for sure, it's on the table still but I could still see this issue as being additive on top of a brass and feed cone depth issue. And because the dimension of feed cone depth looks to be larger than 0.005", then I personally would not rule it out.

[lazyengineer]

From the engineering side, there are basic principles of pressure, axial stress, torsion, loads, factors of safety, metallurgy, etc.

These are all essential to know and be familiar with in firearms engineering, but you really need more specific experience in firearms engineering to understand what is going on.

I’ve seen several people in this industry now, including guys I highly respect who have done extremely well for themselves financially, who made some of the most egregious and erroneous statements about the basics of firearms engineering.

One of them, who went on to start and grow a very popular company, told me to my face that he thinks, “Bolt thrust is bullish*t.”

Bolt thrust is a fundamental reality of basic locking breach repeating firearms, where axial stress is placed on the bolt from the contained pressure in the system.

Same with bolt lug torsion on a rotating bolt design when the gas system is not timed correctly.

Metallic cartridge case metallurgy is also a fundamental discipline, where various manufacturers weigh the engineering and financial trade-offs as to how they will formulate their brass alloys.

Lapua chooses to focus on the best possible metallurgy, combined with tight tolerances on case dimensions internally and externally, with emphasis on measured aspects of flash hole performance relative to primer spark penetration depth into the propellant column.

The cheaper, softer brass manufacturers focus on volume production, so they make design trade-offs relative to areas of the case to keep them within FoS based on the SAAMI MAP, MPSM, and MPLM.

Cartridge manufacturers have to batch-test multiple samples within lots, which are then fired through instrumented and calibrated test breeches.

Reputable component manufacturers do their own testing, the more strenuous, the better their reputations tend to be.

Lapua has been the gold standard in that space for many decades.

A lot of people might read this and constrain my comments to their own situation, where they own and shoot only 1-2 of these firearms in this cartridge.

In reality, I have lost track of how many 6.5 Grendels I have tested over the years, while owning many, ranging from the longer barrels on down to the 12” guns.

I have had nothing but boringly-repeatable results with the Lapua brass. Then again, I’m very discerning about what barrels and chambers I use.

I have given some companies the benefit of the doubt by taking a chance with their barrels, bolts, and chambers.

Some worked out, and others didn’t.

I think this incident is starting to look more and more like a serious excess headspace problem, nothing to do with the brass.

Interestingly enough I too had doubts about "bolt Thrust" at one time, so I did the calculation running the cross sectional area of a case-body wall, and the tensile strength of brass. I had to admit, there is a meaningful degree of force required to stretch brass enough that it likely does decrease force on the bolt lugs' which, while no means the bulk of the force, it was a fairly nontrivial amount. I can't recall exactly, but vaguely I think it was in the 5-10% of force type of range - but don't quote me on that.

Regarding the rest, yes, it is apparent that the case failure main contributing cause was an issues with the chamber/headspace in some manner. Very probably equipment that shouldn't have been cut that way; and I would advise OP to consider hard if his barrel is what he wants to keep - or at least, with Lapua. My own premise, is that other brass manufactures are designed and manufactured with a higher tolerance of error in that zone, and are proving more forgiving to the defect. And me: I value that. I have and have had BBLs from Alexander, PSA, Faxon, BFT Moster, and custom; and bolts from nearly all of them - sometimes mixed around. I don't kaboom - but I don't run Lapua.

My concern is that with Grendel popularity and ammunition unavailabilty, more new users and those less experienced at equipment specification and inspection, are being guided by advise in this forum to a brass brand that is being promoted as the best and safest brass, when that brass is proving via these posts - like it or not - to have the growing body of data as the brass that fails in some settings, when others apparently are not.

The answer continues to be "send me your unsafe Lapua brass", which is a misguiding quip; because it indicates to someone with a random-brand Grendel barrel and random bolt, that Lapua is the endorsed brass they should be buying - where I contend - it is not. It is the brass someone with a quality Alexander arms; BFT Team-Monster, or other known good barrel, should be buying. My own philosophy of safety is to buy and endorse components forgiving of other system and operation failures; if there is no detriment to doing so - and in particular to those less experienced. This passion for safety has been the source of my saying of the unpopular; not a drive To Be Right.

Regarding case-head separation - if you observe closely, the 5.56 casings are designed with a wall thickness that tapers a touch, so that head-space separations are up a good bit, about the overall size of a .380 casing or so. All it takes is just a little bit of case body (not just head) to maintain a seal for safety, and the gun will not explode. This works very well in 5.56 and I have had and seen more 5.56 case head separations over the years than I can count - never a safety incident. With 6.5 Grendel, if you observe the Hornady case design, it follows that philosophy to a degree. It is not apparent to me that Lapua does as agressively. I don't know where a case-head separation normally is in a Lapua Grendel casing, and have concern that it may be low enough to fail to retain enough body to still seal off the walls (though maybe - there is at least some taper, now that I went back to the below picture and checked anew). I one of the Lapua Grendel Kaboom postings in the last year, I have to wonder if that's what happened. Though I can't say. I can say it was - yet again - Lapua brass.



I continue my postulation that in the hands of an experienced reloader with proper equipment, Lapua is an excellent choice that will provide much life, and superior consistency for maximum precision and power. For the general population using general mixed barrels, I do not feel it is sufficiently safely engineered. I support this postulation with 3 Kabooms posts in 12 months, all running Lapua brass. Disregarding that strikes me as disingenuous bias.

[DeNinny]

lazyengineer in looking at that pic again I will add that the thicker base by Hornady not only gives the base more structural strength (all other things equal), it also keeps the powder closer to the shoulder and away from the bolt, and it closes the gap of the unsupported area.

[LRRPF52]

Every single one of those cases has case taper moving down to the web. The farthest on the right was not sectioned and cleaned-up the same way the others were too, if you look closely.

Why would someone go to all the trouble to section 2 samples of each case type, clean the Lapua and Starline up, but then leave the Hornady ragged on the cuts?

The answer continues to be "send me your unsafe Lapua brass", which is a misguiding quip; because it indicates to someone with a random-brand Grendel barrel and random bolt, that Lapua is the endorsed brass they should be buying - where I contend - it is not. It is the brass someone with a quality Alexander arms; BFT Team-Monster, or other known good barrel, should be buying. My own philosophy of safety is to buy and endorse components forgiving of other system and operation failures; if there is no detriment to doing so - and in particular to those less experienced. This passion for safety has been the source of my saying of the unpopular; not a drive To Be Right.

Nobody said "send me your unsafe Lapua brass", because we know it’s safe.

A firearm with excess headspace will cause problems with all of the brass run through it over time. Remember how he had failure to fire/failure to activate primer already, with difficulty extracting that cartridge.

I have never had a failure to activate a primer with any 6.5 Grendel I have owned or tested.

Excessive headspace is a problem, regardless who the manufacturer is. It’s not a special condition for a firearm that only more experienced shooters know how to handle and deal with.

The corrective action is the same for anyone, layman or reloaders with decades of experience: The firearm must be repaired or replaced before shooting anymore.

One way to put this to bed is to see what the headspace is on other ammuntion’s fired brass from that bolt/barrel combo.

[LRRPF52]

lazyengineer in looking at that pic again I will add that the thicker base by Hornady not only gives the base more structural strength (all other things equal), it also keeps the powder closer to the shoulder and away from the bolt, and it closes the gap of the unsupported area.

If the Hornady brass was actually stronger, it wouldn’t lose primer pocket tension after 5-12 loads.

Guess which brand lasts longer than any other brand of brass in 6.5 Grendel? Lapua

I like the Hornady brass a lot, so it isn’t a ding against them, just what I and others have seen with it collectively.

[DeNinny]

If the Hornady brass was actually stronger, it wouldn’t lose primer pocket tension after 5-12 loads.

Guess which brand lasts longer than any other brand of brass in 6.5 Grendel? Lapua

I like the Hornady brass a lot, so it isn’t a ding against them, just what I and others have seen with it collectively.

I'm not ruling out other reasons why Hornady brass loses primer pocket tension. For example it might be due to initial pocket size or even amount of initial swage.

As to your point about Lapua brass lasting longer, I would like to see all the data that supports that point. Like does it last longer for AR users and is there a difference on how long it lasts for bolt action users and AR users as compared to Hornady and other brass. Also what are its materials science properties parameters. Like Young's modulus, tensile strength, shear modulus, and hardness. And lastly what are the failure rate differences between brass. Like how many blowouts are occurring between all the manufacturers.

[stonehog]

Stone.thanks for posting.
None of this is worth getting hurt over.SAFETY FIRST.
I've noticed earlier in your post and the last one that the original bolt didn't pass headspace after kaboom.It couldn't have grown/shrunk,unless chunks are missing.
You said it's an Odin barrel.Is it an Odin bolt?Odin and some toolcraft/psa bolts were 2.80" long and used a shorter firing pin.Standard grr bolts are 2.81" and use a milspec pin.
You said some of your brass measured .001 less than fired brass.Semi autos need .003 bump min.
Sooo.Possible cause.
1.headspace
2.to long a case.
3.milspec pin in an Odin bolt
Any one, oob assplosion
Or,POS piece of brass.

I've been loading unsized unfired bass.Never again.
Thank you sir,You might have kept me from hurting me.or others.

It is an Odin barrel and Odin bolt - I believe I put it in a PSA BCG, but will have to check. I will be able to measure the bolt in a few days - will post.

[LRRPF52]

Thank you for that dimension. Just using your numbers, I get .138" - .133" = 0.005" difference. And so if I understand your position correctly, you are saying that, in this scenario, the OPs casing was roughly 0.005" more unsupported, and possibly more if you add headspace. And this distance is what is considered dangerously excessive?

To me, for sure, it's on the table still but I could still see this issue as being additive on top of a brass and feed cone depth issue. And because the dimension of feed cone depth looks to be larger than 0.005", then I personally would not rule it out.

I’m not following those numbers. I’m not sure what you’re saying, so it might just be me.

The deeper the bolt face, the longer the headspace.

Grendel bolts should be no deeper than .136”, but can be .003” shallower (.133”). Chambering will be more difficult and not repeatable under some conditions if you go less than .133”.

Chambering will be easier with deeper than .136” (out of spec), but then the case web won’t be supported and you can have things like this.

Most bolts I’ve measured were either .136” or .135”, but I do recall one that was .137” that probably shouldn’t have left the vendor.

Once you start exceeding the dimensions, tolerance stacking can occur and create unsafe headspace.

[Klem]

Lots of discussion here about Lapua brass and frankly I think it has gone sideways into a strawman argument thanks to the persistent arguing of one person (no offence). Just because the case has the most visible indication that something went wrong does not mean it was the cause of it.

We still don't know whether this was an in-battery or out-of-battery situation, and we also don't know whether headspace was in spec prior to firing. Headspace of the chamber/bolt combo, and headspace of the loaded case. We only know headspace is out of spec now. For a bolt to be in one piece after a catastrophic failure; the extractor is still OK, but out of spec now with a NO GO gauge introduces one possibility that the bolt was out of spec to begin with.

Another piece of info is the stretch of spent cases is .001", which is typical of bolt gun sizing. This introduces the possibility that the blown case might have had so little headspace that it interfered with the bolt trying to close. Yet closed enough to permit firing.

The load was compressed, and whether we think the amount is 'hot' or 'OK' is less important than it was compressed, with all that implies about changing expected pressures.

Regardless, I think we should move away from Lapua being a suspect brass manufacturer - for the simple reason they are not. Something other than brass manufacturer caused this.