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

[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.