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

[DeNinny]

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

Agreed and appreciated. LOL I work with all kinds of engineers and technical people, and trust me they all can have differing opinions about diagnosing the same problem. This exchange is a typical day at work for me. The only (obvious) rule for everyone is to use data and the laws of science to back your position. And be open to being mistaken on your own understanding.

Also, being new here and coming from Reddit, there is absolutely no way I could get technical over there like I am here. Over here, I'm with my people. We are all part of the Horde and so we are all on the same team! And we don't even have to agree on everything. That's no fun.

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.

Understood on all. The 5.56 cartridge is also smaller diameter than grendel, so absolutely it will withstand higher pressures than grendel (all other things equal). The lower radius and lower size to brass volume ratio makes it stronger on a pound-for-pound basis. Again it's like an archway analogy that I mentioned before.

So with this I'm sorry I stated that the grendel round had to be designed to withstand higher pressures. That was incorrectly phrased. What I really meant is that its less curved case wall due to higher diameter needed to have more support. Hence, the Bill Alexander feed cone redesign. I hope we are on the same page about it now. Again, I never cared about the pressure itself. I only cared about what Bill Alexander was addressing when he redesigned the feed cone.

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.

The data I'm looking for here is the failure (or lack thereof) data for Lapua brass used with M16 style feed cone barrels in AR15 platforms. And I'm also looking for comparison data on this amongst all the various grendel brass manufacturers. I always need the comparison data! Not just one manufacturer's.

It doesn’t matter what the metallurgical details are when we can see the actual performance.

And again I don't see comparative actual performance data under the specific condition of this failure. And in lieu of not having this data, the next best thing to me is to have the specific materials science parameters that I mentioned...Young's modulus, shear modulus, hardness, yield strength.

And I know all this data is a tall order and will likely never be produced. And this is why I'm leaving the conclusion open ended. I'm not saying it's definitely Lapua brass as a contributing issue, and I'm not not saying it too!