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

[StoneHendge]

Everyone here is neglecting the likelihood of human error in the barrel manufacturing process. Drill the feed cones too deep and kaboom.

[DeNinny]

Thanks grayfox. Klem posted the article earlier. The problem with it is that it is still inconclusive. And the commentator posts make sense, BUT...they are mostly only talking about the permanent deformation properties of metal and the other factor to consider are the temporary deformation properties. When an alloy gets harder and has higher yield strength, it can also get more brittle or inelastic. This is why Young's modulus and shear modulus are other important parameters in addition to hardness and yield strength. This is why I want the hard numbers of everything. Chemical composition only gives partial information.

In short, the article helps to a degree, but it still doesn't provide conclusive proof that Lapua brass is "better". Hence, that big disclaimer you quoted from it.

[DeNinny]

Everyone here is neglecting the likelihood of human error in the barrel manufacturing process. Drill the feed cones too deep and kaboom.

That's the first point of my failure model! I have not neglected this...

"...it's a tolerance stacking issue...the barrel feed cone was too long,..."

Edit: To me, in hindsight, and because Bill Alexander expressed it as a necessary design change from the M16 feed cone, I don't understand why he didn't make that a specification. At least create a maximum depth spec. This is in hindsight, but I think it needs a spec.

[lazyengineer]

Thanks grayfox. Klem posted the article earlier. The problem with it is that it is still inconclusive. And the commentator posts make sense, BUT...they are mostly only talking about the permanent deformation properties of metal and the other factor to consider are the temporary deformation properties. When an alloy gets harder and has higher yield strength, it can also get more brittle or inelastic. This is why Young's modulus and shear modulus are other important parameters in addition to hardness and yield strength. This is why I want the hard numbers of everything. Chemical composition only gives partial information.

In short, the article helps to a degree, but it still doesn't provide conclusive proof that Lapua brass is "better". Hence, that big disclaimer you quoted from it.

Yes. There is little questin Lapua brass metallurgy is great. But no case wall is strong enough to hold back 52,000 psi on its own, if there is no steel chamber there. A case head, does, every shot. Lapua runs a thinner case head, and if the chamber isn't cut quite right, appears to be the first to expose case wall and fail, we seem to see.

[DeNinny]

Yes. There is little questin Lapua brass metallurgy is great. But no case wall is strong enough to hold back 52,000 psi on its own, if there is no steel chamber there. A case head, does, every shot. Lapua runs a thinner case head, and if the chamber isn't cut quite right, appears to be the first to expose case wall and fail, we seem to see.

Agreed. And this is speculation only, but a more malleable and/or elastic brass that may not have the same hardness or yield strength as Lapua might still be "better" for this failure. Instead of the metal tearing and rupturing to create a blowout, it *might* just stretch like a balloon instead. The evidence is anecdotal only but the snipershide thread linked earlier showed pics of Hornady brass with the belt phenomena. No tearing or blowout holes. Just extremely stretched brass. Again, speculation only but maybe, just maybe, Hornady brass is easier to stretch but not tear than Lapua.

[LRRPF52]

So I forgot that you had some data here regarding the feed cone specs. And it's very helpful in this analysis. But it's not perfect. So I have to make some assumptions which I will clarify along the way. Here goes...

To start, I've been wanting an approximate size of the feed cone depth because we are all mostly in agreement that this is the unsupported area of the case and the failure occurred at an unsupported area. Also remember that Bill Alexander himself stated that he had to reduce it for the grendel round. And per the note above..."the edges are radiused .0625"...I think this is a good starting approximation of the standard M16 feed cone depth which supposedly is the same for an Odinworks barrel. I'll note that it is not perfect, but I'm pretty sure the feed cone depth will be approximately close to this dimension.

Next, I want to compare this to the feed cone depth of an Alexander Arms barrel. But unfortunately, it was stated that this is proprietary information, so we will have to make an assumption here. And remember that Bill stated that this change was critical to the design because of the high pressure in the grendel round. So if it was this important, I think we could assume that he made at least a 30% improvement to reducing the size of the feed cone depth. So taking 70% of 0.0625", I am getting 0.7 x 0.0625" = 0.04375”.

6.5 Grendel isn’t a relatively high pressure round for modern cartridges. It has a much lower Maximum Average Pressure than 5.56x45, .308 Winchester, and other rifle cartridges that have been developed over the last 30 years. Most of your factory ammunition is running in the 47,000-49,500psi range, with MPSMs that can’t exceed 52,000psi. These pressures were more common from the late 1800s-1950s, for reference.

At this point I want to mention that the excessive head space issue is in the wrong direction with respect to exposing the brass to unsupported wall area. Excessive head space is at the shoulder end of the case and allows the round to go more into the chamber rather than out of it. As such, I'm not accounting for this in my math and moreover I don't think it is a viable failure model...but I'm open to being convinced otherwise.

Excessive headspace can be caused by a combination of shoulder location and incorrect (too deep) bolt face depth. The brass grows to fill the void, since cartridge brass is so soft (Alloy 260 ~70/30 Copper/Zinc). Brass is just a high pressure gasket designed to hold the primer, propellant, and projectile together for repeating firearms for easy storage, transport, and stacking in feed devices. The chamber pressure immediately swells it into the shape of the chamber and bolt, from which it rebounds some back between its original shape and the obturated shape. Different brass manufacturers have their proprietary processes that create stronger brass, or easier to mass-produce brass. Lapua brass is known around the world for decades to have the strongest construction, last for the most reloads, and have the smallest SDs in weight, volume, neck thickness, flash hole geometry, etc.

So during many excess headspace scenarios, the vast majority of the pressure is contained well within the chamber, but as the brass finishes its rearward growth, it stretches past the point of full chamber support, and there is enough residual pressure to blow out the now-exposed portion of brass. Since the extractor is still intact, that steers us towards excess headspace and not an over-pressure event. When you have case failures in the AR-15, it’s very common to have extractors destroyed. (A sidebar anecdote on this is that Hk placed a pin inside the barrel extension in the extractor clock location to help prevent this from happening on the Hk416.)

Now as to the brass itself. It definitely plays a role here and cannot be dismissed as well. With more unsupported brass exposed, weaker brass will tend to fail more often, and stronger brass will tend to fail less. To this point, the first question I have is...would the OP have had the same failure with Hornady or another brass besides Lapua? To this issue, it is still undetermined. But it is entirely possible. I know some folks are saying no way it was due to Lapua brass, but I'm sorry that's not being very objective without numerical evidence. We have 3 threads on this forum alone that are of Lapua grendel brass failing. We have Bill Alexander saying that he designed the grendel working with Lapua brass and he outright states that he had to change the feed cone design to limit the amount of unsupported brass with it. We also have visual proof that Lapua has less overall brass around the case head. (And the only counterarguments to this are non-numerical claims..."Lapua is the gold standard of brass"..."I've used Lapua brass for years without problems"...etc.)

I don’t think we can say that Lapua brass definitely played a role in this. The only possibility there would be this particular piece of brass, not Lapua as a whole, and even that’s a stretch.

Lapua 6.5 Grendel brass fleet experience at this time is in the millions of samples in production-who knows how many times those have been reloaded. Bill’s initial work was one of the only smaller companies that actually did pyramid testing on his rifles not just for reliability, but for accuracy and durability. In addition to that, he did high sand/dust testing regularly, flying out to a large training center in New Mexico where the surface is covered in sharp rocks, sand, and dust. If any of you recall the Future Weapons episode on 6.5 Grendel with “Mack”, it was filmed there. That was all done with Lapua brass loaded cartridge by Alexander Arms. 6.5 Grendel wasn’t some small project with minimal testing, but an unusually-extensive and professionally-executed developmental program for a non-big-named company at the time.

So Lapua brass isn’t a new, unproven, or anecdotal report-based “it works for me” component in this equation. It was already well-established in the 2000s due to extensive design, testing, and proven performance in large production. That has only grown exponentially since then. Janne Pohjoispaa of Lapua, who was instrumental in the development of .338 Lapua Magnum and 6.5x47 Lapua (superior design compared to 6.5Creedmoor), was the lead engineer in developing the finer details of 6.5 Grendel brass, working in conjunction with Bill Alexander. These are not only formally school-trained engineers specific to firearms and ammunition, but both had many years of experience prior to this developing cartridges for military and industry requirements. Bill worked on the UK’s answer to the NATO PDW requirement with a cartridge called the .224 Boz, was trained within UK MoD how to do depot-level inspection and maintenance overhauls on AR-15s in UK service (by Eugene Stoner and other senior engineers), did .50 Beowulf, 5.45x39 in the AR-15 (.221 Genghis), and then 6.5 Grendel.

Another aspect of the inherent design soundness of 6.5 Grendel brass was how smoothly the SAAMI certification process went. Normally with SAAMI, if they find problems with your design, they will kick it back, because even among the large ammunition and firearms manufacturers, mistakes are made during the design process, schematic drawings, pressure ratings, angles, radii, wall and neck thicknesses, alloys, etc. 6.5 Grendel development was unusually stacked with very experienced designers from 2 of the most well-respected firearms and cartridge engineering cultures.

Many of the reference rifles used in velocity testing, in conjunction with pressure test breeches, were Alexander Arms AR-15s. For example, Hornady’s sample rifles include 14.5” and 18” AA AR-15 carbines. I have personally confirmed this with Hornady’s engineers, who went and looked in their armory to verify those test rifles for the 8th, 9th, and subsequent editions of their load manuals.

And finally, we have the OP using Lapua brass with an Odin barrel which has the M16 feed cone design that Bill Alexander intentionally redesigned for the grendel round.

So with all that said, all my earlier failure models are on the table and I'm in alignment with lazyengineer that it's a tolerance stacking issue...the barrel feed cone was too long, the brass was too weak*, there was too much powder, and (possibly) the bolt face was too deep. All these combined led to the failure.

*And note that by brass being too weak, I'm open to the fact that there may have been a defect in it and/or other factors besides that it was simply Lapua brass.

I already addressed the hypothesis of too much propellant earlier. 29.x grains of AA2520 under a 123gr cup and core bullet is not the max load with a chamber with his measurements.

Hornady’s published loads for AA2520 are limited by the Monolithic 120gr GMX, which is longer than some of the 140gr cup and core bullets. That limits case capacity due to intrusion, and also resists being driven into the lands more than cup and core bullets. His stated load is well under max, which is likely why we didn’t see the extractor blow out, primer intact, case head looking ok other than the failure in the side of the brass.

Everything really points to excessive headspace. No other variable is needed or indicated from what I’m seeing here, not having the components in my hands.

[Klem]

Lapua runs a thinner case head, and if the chamber isn't cut quite right, appears to be the first to expose case wall and fail, we seem to see.

Once again the thin vs. thick brass assumption creeps back in. There is nothing 'appears' about it - it is pure speculation. We do not know the relative strengths of Hornady vs. Lapua. We may never know what caused that case to burst.

[LRRPF52]

Thanks grayfox. Klem posted the article earlier. The problem with it is that it is still inconclusive. And the commentator posts make sense, BUT...they are mostly only talking about the permanent deformation properties of metal and the other factor to consider are the temporary deformation properties. When an alloy gets harder and has higher yield strength, it can also get more brittle or inelastic. This is why Young's modulus and shear modulus are other important parameters in addition to hardness and yield strength. This is why I want the hard numbers of everything. Chemical composition only gives partial information.

In short, the article helps to a degree, but it still doesn't provide conclusive proof that Lapua brass is "better". Hence, that big disclaimer you quoted from it.

When seasoned, older reloaders who put high load counts on brass say, “This one gets up to 50 reloads and others don’t even approach that.”, that’s a pretty huge indicator of the quality of one brass over others.

Early-on with 6.5 Grendel, we had guys on the forum who got 20 or more loads with Lapua brass, shot the headstamps out. No other brass that I’m aware of has achieved that many loads.

When I have shot and reloaded Federal 6.5 Grendel brass, for example, I lost primer pockets within 2 loads when shooting through the AR-15.

Interestingly, this did not happen when shooting and loading it through the Howa Mini bolt-action rifle. Even with me loading well over 1-2 grains higher than book loads in the AR-15, the primer pockets stayed nice and tight in the Howa with Federal brass.

Hornady brass has been the next-best performer for me in terms of longevity, number of reloads.

Other seasoned reloaders here on the forum have reported as many as 8-12 loads. Depending on what dies, pressures, gas system lengths, and chambers are used, you might see that brass become unusable at 5 loads.

This catastrophic failure happened with new Lapua brass on his first firing of that batch, #41 of 50 hand-loaded cartridges.

That brings me to the question, can we see the heads of the 40 other fired pieces of brass if we haven’t seen them already?

[DeNinny]

6.5 Grendel isn’t a relatively high pressure round for modern cartridges. ...


...

I don’t think we can say that Lapua brass definitely played a role in this. The only possibility there would be this particular piece of brass, not Lapua as a whole, and even that’s a stretch.

...

I will get to your other points later tonight. In short I'm sorry but I don't agree it's exclusively head space. I will get you my logic later.

On grendel brass pressure I understand what you posted, but I'm just saying it was high enough or different enough that Bill Alexander sought to redesign the feed cone depth because of it. That's all I meant. The pressure of a grendel round was enough to be different from that of a 5.56 round that he knew he had to change the feed cone design to account for it. That's it. I don't really care about the spec value either. I care about what Bill Alexander said about it.

Once again I never said Lapua brass played a role! I said 'weaker brass' played a role. Left out the 'Lapua' intentionally. Also I'm saying that you can't rule it out.

Lastly, I'll note that in all your talk about Lapua brass you don't provide any numerical information that quantifies it as better. But more on this later...

[DeNinny]

LRRPF52 I'm pretty sure it was round #41 according to OP's first post.

[grayfox]

This catastrophic failure happened with new Lapua brass on his first firing of that batch, #4 of 50 hand-loaded cartridges.

That brings me to the question, can we see the heads of the 3 other fired pieces of brass if we haven’t seen them already?

I believe he said #41 out of 50...
But your point is well taken, what about the 3-4 preceding rounds? Also, we don't know how many fired, what rest time in between groups or individual rounds, maybe OP can fill us in.
At any rate, preceding rounds might give some insight.

Again, as to Lapua, in the AccurateShooter article it states that the older, muntz metal, brown box Lapua was reported to be very long-lasting... one cannot infer any one brass is better or worse (this from several metallurigists he queried) so all together, in my opinion any conclusions about metal or strength or brand, are speculative at best. The only physical thing we know is that it is thinner in design at the bottom curvature between wall and base.
Headspace, which develops into space at the back of the round after metal has expanded forward to fill the chamber volume (if I have that right), non-supporting cone-depth/shape/design, other tolerances combined- could translate to a too-long exposure of metal to hot pressurized gas, with possibly the bolt pulling away "early" due to unlocking sequence of a 12"/carbine barrel (ejecting at a higher pressure than a rlgs for ex)... at some point the combination got to the point where one case failed.

I would think that 2 or 3 of the preceding cases would also show some kind of beginning fail/incipience or imminent issue... if it were a purely mechanical/repeatable scenario.

Mention made of the millions of lapua rounds, so we also need to admit that these are the only reported instances. How many were unreported? How many unreported from other vendors'? Without some kind of methodical study even on this combo, it would be premature to point the finger at any single component, or even any single sequence of events. It is troubling for sure, but on balance, I don't see any generalizations honestly coming from what we know at this point.

[LRRPF52]

I will get to your other points later tonight. In short I'm sorry but I don't agree it's exclusively head space. I will get you my logic later.

On grendel brass pressure I understand what you posted, but I'm just saying it was high enough or different enough that Bill Alexander sought to redesign the feed cone depth because of it. That's all I meant. The pressure of a grendel round was enough to be different from that of a 5.56 round that he knew he had to change the feed cone design to account for it. That's it. I don't really care about the spec value either. I care about what Bill Alexander said about it.

Once again I never said Lapua brass played a role! I said 'weaker brass' played a role. Left out the 'Lapua' intentionally. Also I'm saying that you can't rule it out.

Lastly, I'll note that in all your talk about Lapua brass you don't provide any numerical information that quantifies it as better. But more on this later...

We’re just talking ideas here, not picking anyone person apart, so be assured this isn’t personal.

5.56x45 is loaded to higher pressures than 6.5 Grendel. The case geometry for 6.5 Grendel is considerably different than 5.56x45, which required numerous design changes in the bolt, extractor, tighter tolerances held on the barrel extension (due to warping from heat-treating that is fine with 5.56 but not Grendel), magazines, etc. I’ve had pretty extensive discussions with Bill about this offline over the years. The things he covered are aspects of the rifle and cartridge he learned the hard way during development, on top of formal engineer training and experience with his prior work. It’s a fascinating story really.

None of these design nuances are secret, since anyone could order AA Barrel/bolt combos and rifles to inspect if they wanted to back then.

I provided numerical data, namely the fact that millions of 6.5 Grendel Lapua brass and ammunition have been manufactured and fired and reloaded from 2004-present.

It doesn’t matter what the metallurgical details are when we can see the actual performance. People have done metallurgical analyses, but this doesn’t tell you what processes are used by Lapua, and doesn’t explain why reloaders get more loads on Lapua brass than other brands, including those who shoot and load it in AR-15s in various chamberings. You can do spectral analysis, but that only tells you the alloy composition, not processes.

Same thing with AR-15 bolts. I can provide the same exact alloy stock to 2 different machine shops, tested and certified before shipping.

1 shop will crank out a great bolt that lasts 10,000-25,000 rounds.
The other will fail at 5,000 rounds.

Both got the exact same alloy from the same batch. Both machined them to the exact same dimensions, in the same exact same order of operations.

One heat-treated differently and did their batch-testing differently.

The other did High Pressure Test and MPI on all of theirs after their own heat-treating specs.

Heat-treating and other processes create varying levels of durability.

Testing will expose the weaknesses of one, and the strengths of the other.

Notice that with one of the alloys used in older brown box Lapua (my original batch of Lapua brass is from that era), the conventional wisdom said that copper/zinc ratio should have been weaker, but resulted in 50 loads for the particular Bench Rest reloader.

Maybe Lapua knows a thing or two about their processes that other brass-makers don’t, or won’t use because of costs and their specific tooling.

[LRRPF52]

This photo is really odd to me. Does anyone else see what I’m seeing?

Notice that the alleged Hornady brass samples on the right are much taller, and the sectioning hasn’t been cleaned up like it has on the Lapua and Starline cases.

Reason I noticed is because I’m used to looking at sectioned pieces, and have had cases professionally sectioned for me by an exotic alloys metallurgist and engineer who does funded studies on medical devices, as well as being a doubly-trained gunsmith and competitive shooter and reloader. This guy uses digitally-enhanced Zeiss microscopes to analyze and photograph microscopic laser weld deformation on exotic alloys like NITINOL for his profession, specifically failure node analyses and materials inspections.

The Lapua and Starline cases have their cut lines cleaned up pretty well. The Hornady cases have jagged and folded edges, particularly around the areas of the case on the base and web. We can’t really make conclusions based on this photo for that reason, because the sectioning process is not consistent across the alleged brass types just from a dimensional perspective, let alone metallurgy and processes.

[lazyengineer]

This photo is really odd to me. Does anyone else see what I’m seeing?

Notice that the alleged Hornady brass samples on the right are much taller, and the sectioning hasn’t been cleaned up like it has on the Lapua and Starline cases.

Reason I noticed is because I’m used to looking at sectioned pieces, and have had cases professionally sectioned for me by an exotic alloys metallurgist and engineer who does funded studies on medical devices, as well as being a doubly-trained gunsmith and competitive shooter and reloader. This guy uses digitally-enhanced Zeiss microscopes to analyze and photograph microscopic laser weld deformation on exotic alloys like NITINOL for his profession, specifically failure node analyses and materials inspections.

The Lapua and Starline cases have their cut lines cleaned up pretty well. The Hornady cases have jagged and folded edges, particularly around the areas of the case on the base and web. We can’t really make conclusions based on this photo for that reason, because the sectioning process is not consistent across the alleged brass types just from a dimensional perspective, let alone metallurgy and processes.

Probably to some degree - but the gist is consistent with other statements and measurements that Lapua has a higher case capacity. Not really that controversial.

[DeNinny]

Remember there's another pic too with Lapua, Starline, and Hornady in the pics from the snipershide thread linked earlier. It also showed the same thing with Hornady having the thickest brass at the head and Lapua having the least. Starline was in between.

[Fess]

Back when I worked for a company that produced pneumatic valves and hydraulic lifters (lash adjusters) for the automotive market, the cross sections were done differently. The parts were immersed in a "puck" of thin epoxy resin, under vacuum (to eliminate air bubbles), then cut by a diamond-tipped saw blade. This gave a very clear cross-section.
I agree that many of the cross-sections of cases seen in the interwebs are next to useless.

[lazyengineer]

Once again the thin vs. thick brass assumption creeps back in. There is nothing 'appears' about it - it is pure speculation. We do not know the relative strengths of Hornady vs. Lapua. We may never know what caused that case to burst.

It never creeped out - and there is no speculation- it's staring us in the face, and the heavily quoted Alexander confirms that a chamber dimension needs to be just so with that brass. Walls don't hold pressure, they are a gasket. Case heads hold pressure. No case head where there is no chamber wall = not holding pressure.

[StoneHendge]

That's the first point of my failure model! I have not neglected this...

"...it's a tolerance stacking issue...the barrel feed cone was too long,..."

Edit: To me, in hindsight, and because Bill Alexander expressed it as a necessary design change from the M16 feed cone, I don't understand why he didn't make that a specification. At least create a maximum depth spec. This is in hindsight, but I think it needs a spec.

It's got nothing to do with the spec. The manufacturer likely effed up making the barrel. We've seen it here countless times on here barrel issues which were likely due to reaming too shallow or too deep. Easy enough to do with whatever tool they do the feed cone with too.

[grayfox]

[ATTACH=CONFIG]19135[/ATTACH]

somehow this pic failed to post up there...
from Accurate Shooter article.

[JASmith]

Hornady says 29.1 grains is max with that combo, but both QL and GRT say that's a 64,000 plus PSI load.

Nosler says 29.5 grains with their 120 gr BT.

Weird.

Those who use QL or GRT to tell if a load is safe will sooner or later get a nasty surprise.

I have done enough calculations against published data to know that.

It is all the more insidious because QL generally over-predicts pressures for the Grendel. The few times where the pressure is under-predicted are where the nasty surprises lurk. . .