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

[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.